diff --git a/lib/iris/_concatenate.py b/lib/iris/_concatenate.py
index 418cf86554..9f37fd24b2 100644
--- a/lib/iris/_concatenate.py
+++ b/lib/iris/_concatenate.py
@@ -330,7 +330,6 @@ def __init__(self, cube):
 
         self.defn = cube.metadata
         self.data_type = cube.dtype
-        self.fill_value = cube.fill_value
 
         #
         # Collate the dimension coordinate metadata.
@@ -675,8 +674,6 @@ def concatenate(self):
                                   dim_coords_and_dims=dim_coords_and_dims,
                                   aux_coords_and_dims=aux_coords_and_dims,
                                   cell_measures_and_dims=new_cm_and_dims,
-                                  dtype=cube_signature.data_type,
-                                  fill_value=cube_signature.fill_value,
                                   **kwargs)
         else:
             # There are no other source-cubes to concatenate
@@ -722,13 +719,6 @@ def register(self, cube, axis=None, error_on_mismatch=False,
 
         # Check for compatible coordinate signatures.
         if match:
-            fill_value = self._cube_signature.fill_value
-            # Determine whether the fill value requires to be
-            # demoted to the default value.
-            if fill_value is not None:
-                if cube_signature.fill_value != fill_value:
-                    # Demote the fill value to the default.
-                    self._cube_signature.fill_value = None
             coord_signature = _CoordSignature(cube_signature)
             candidate_axis = self._coord_signature.candidate_axis(
                 coord_signature)
diff --git a/lib/iris/_data_manager.py b/lib/iris/_data_manager.py
index 5659604d3b..fdda7e24cd 100644
--- a/lib/iris/_data_manager.py
+++ b/lib/iris/_data_manager.py
@@ -37,7 +37,7 @@ class DataManager(object):
 
     """
 
-    def __init__(self, data, fill_value='none', realised_dtype=None):
+    def __init__(self, data):
         """
         Create a data manager for the specified data.
 
@@ -48,40 +48,14 @@ def __init__(self, data, fill_value='none', realised_dtype=None):
             real data, or :class:`~dask.array.core.Array` lazy data to be
             managed.
 
-        Kwargs:
-
-        * fill_value:
-            The intended fill-value of :class:`~iris._data_manager.DataManager`
-            masked data. Note that, the fill-value is cast relative to the
-            dtype of the :class:`~iris._data_manager.DataManager`.
-
-        * realised_dtype:
-            The intended dtype of the specified lazy data, which must be
-            either integer or boolean. This is to handle the case of lazy
-            integer or boolean masked data.
-
         """
         # Initialise the instance.
-        self._fill_value = None
         self._lazy_array = None
         self._real_array = None
-        self._realised_dtype = None
 
         # Assign the data payload to be managed.
         self.data = data
 
-        # Set the lazy data realised dtype, if appropriate.
-        self._realised_dtype_setter(realised_dtype)
-
-        default_fill_value = (isinstance(fill_value, six.string_types) and
-                              fill_value == 'none')
-
-        # Set the fill-value, must be set after the realised dtype.
-        if ma.isMaskedArray(data) and default_fill_value:
-            self._propagate_masked_data_fill_value()
-        else:
-            self.fill_value = None if default_fill_value else fill_value
-
         # Enforce the manager contract.
         self._assert_axioms()
 
@@ -134,11 +108,8 @@ def __eq__(self, other):
         if isinstance(other, type(self)):
             result = False
             same_lazy = self.has_lazy_data() == other.has_lazy_data()
-            same_fill_value = self.fill_value == other.fill_value
-            same_realised_dtype = self._realised_dtype == other._realised_dtype
             same_dtype = self.dtype == other.dtype
-            if same_lazy and same_fill_value and same_realised_dtype \
-                    and same_dtype:
+            if same_lazy and same_dtype:
                 result = array_equal(self.core_data(), other.core_data())
 
         return result
@@ -171,18 +142,8 @@ def __repr__(self):
         Returns an string representation of the instance.
 
         """
-        fmt = '{cls}({data!r}{fill_value}{dtype})'
-        fill_value = ''
-        dtype = ''
-
-        if self.fill_value is not None:
-            fill_value = ', fill_value={!r}'.format(self.fill_value)
-
-        if self._realised_dtype is not None:
-            dtype = ', realised_dtype={!r}'.format(self._realised_dtype)
-
-        result = fmt.format(data=self.core_data(), cls=type(self).__name__,
-                            fill_value=fill_value, dtype=dtype)
+        fmt = '{cls}({data!r})'
+        result = fmt.format(data=self.core_data(), cls=type(self).__name__)
 
         return result
 
@@ -198,27 +159,8 @@ def _assert_axioms(self):
         state = is_lazy ^ is_real
         assert state, emsg.format('' if is_lazy else 'no ',
                                   '' if is_real else 'no ')
-        # Ensure validity of realised dtype.
-        state = (self._realised_dtype is None or
-                 self._realised_dtype.kind in 'biu')
-        emsg = 'Unexpected realised dtype state, got {!r}'
-        assert state, emsg.format(self._realised_dtype)
-
-        # Ensure validity of lazy data with realised dtype.
-        state = self.has_lazy_data() or self._realised_dtype is None
-        emsg = ('Unexpected real data with realised dtype, got '
-                'real data and realised {!r}.')
-        assert state, emsg.format(self._realised_dtype)
-
-        state = not (self.has_lazy_data() and
-                     self._lazy_array.dtype.kind != 'f' and
-                     self._realised_dtype is not None)
-        emsg = ('Unexpected lazy data dtype with realised dtype, got '
-                'lazy data {!r} and realised {!r}.')
-        assert state, emsg.format(self._lazy_array.dtype, self._realised_dtype)
-
-    def _deepcopy(self, memo, data=None, fill_value='none',
-                  realised_dtype='none'):
+
+    def _deepcopy(self, memo, data=None):
         """
         Perform a deepcopy of the :class:`~iris._data_manager.DataManager`
         instance.
@@ -234,12 +176,6 @@ def _deepcopy(self, memo, data=None, fill_value='none',
             Replacement data to substitute the currently managed
             data with.
 
-        * fill_value:
-            Replacement fill-value.
-
-        * realised_dtype:
-            Replacement for the intended dtype of the realised lazy data.
-
         Returns:
             :class:`~iris._data_manager.DataManager` instance.
 
@@ -251,81 +187,13 @@ def _deepcopy(self, memo, data=None, fill_value='none',
                     data = copy.deepcopy(self._lazy_array, memo)
                 else:
                     data = self._real_array.copy()
-            else:
-                # Check that the replacement data is valid relative to
-                # the currently managed data.
-                DataManager(self.core_data()).replace(data)
-                # If the replacement data is valid, then use it but
-                # without copying it.
-
-            if isinstance(fill_value, six.string_types) and \
-                    fill_value == 'none':
-                fill_value = self.fill_value
-
-            if isinstance(realised_dtype, six.string_types) and \
-                    realised_dtype == 'none':
-                realised_dtype = self._realised_dtype
-
-            result = DataManager(data, fill_value=fill_value,
-                                 realised_dtype=realised_dtype)
+            result = DataManager(data)
         except ValueError as error:
             emsg = 'Cannot copy {!r} - {}'
             raise ValueError(emsg.format(type(self).__name__, error))
 
         return result
 
-    def _propagate_masked_data_fill_value(self):
-        """
-        Align the data manager fill-value with the real masked array
-        fill-value.
-
-        """
-        data = self._real_array
-        if ma.isMaskedArray(data):
-            # Determine the default numpy fill-value.
-            np_fill_value = ma.masked_array(0, dtype=data.dtype).fill_value
-            if data.fill_value == np_fill_value:
-                # Never store the numpy default fill-value, rather
-                # represent this by clearing the data manager fill-value.
-                self.fill_value = None
-            else:
-                # Propagate the masked array fill-value to the data manager.
-                self.fill_value = data.fill_value
-
-    def _realised_dtype_setter(self, realised_dtype):
-        """
-        Set the intended dtype of the realised lazy data. This is to support
-        the case of lazy masked integral and boolean data in dask.
-
-        Args:
-
-        * realised_dtype:
-            A numpy :class:`~numpy.dtype`, array-protocol type string,
-            or built-in scalar type.
-
-        """
-        if realised_dtype is None:
-            self._realised_dtype = None
-        else:
-            realised_dtype = np.dtype(realised_dtype)
-            if realised_dtype != self.dtype:
-                if not self.has_lazy_data():
-                    emsg = ('Cannot set realised dtype, no lazy data '
-                            'is available.')
-                    raise ValueError(emsg)
-                if self._lazy_array.dtype.kind != 'f':
-                    emsg = ('Cannot set realised dtype for lazy data '
-                            'with {!r}.')
-                    raise ValueError(emsg.format(self._lazy_array.dtype))
-                if realised_dtype.kind not in 'biu':
-                    emsg = ('Can only cast lazy data to an integer or boolean '
-                            'dtype, got {!r}.')
-                    raise ValueError(emsg.format(realised_dtype))
-                self._realised_dtype = realised_dtype
-
-                # Check the manager contract, as the managed dtype has changed.
-                self._assert_axioms()
-
     @property
     def data(self):
         """
@@ -338,14 +206,11 @@ def data(self):
         if self.has_lazy_data():
             try:
                 # Realise the lazy data.
-                result = as_concrete_data(self._lazy_array,
-                                          nans_replacement=ma.masked,
-                                          result_dtype=self.dtype)
+                result = as_concrete_data(self._lazy_array)
                 # Assign the realised result.
                 self._real_array = result
                 # Reset the lazy data and the realised dtype.
                 self._lazy_array = None
-                self._realised_dtype = None
             except MemoryError:
                 emsg = ('Failed to realise the lazy data as there was not '
                         'enough memory available.\n'
@@ -354,10 +219,6 @@ def data(self):
                         'before trying again.')
                 raise MemoryError(emsg.format(self.shape, self.dtype))
 
-        if ma.isMaskedArray(self._real_array):
-            # Align the numpy fill-value with the data manager fill-value.
-            self._real_array.fill_value = self.fill_value
-
         # Check the manager contract, as the managed data has changed.
         self._assert_axioms()
 
@@ -412,18 +273,6 @@ def data(self, data):
             self._lazy_array = None
             self._real_array = data
 
-        # Always reset the realised dtype, as the managed data has changed.
-        self._realised_dtype = None
-
-        # Reset the fill-value appropriately.
-        if init_done:
-            if ma.isMaskedArray(data):
-                # Align the data manager fill-value with the numpy fill-value.
-                self._propagate_masked_data_fill_value()
-            else:
-                # Clear the data manager fill-value.
-                self.fill_value = None
-
         # Check the manager contract, as the managed data has changed.
         self._assert_axioms()
 
@@ -433,32 +282,7 @@ def dtype(self):
         The dtype of the realised lazy data or the dtype of the real data.
 
         """
-        if self._realised_dtype is not None:
-            result = self._realised_dtype
-        else:
-            result = self.core_data().dtype
-
-        return result
-
-    @property
-    def fill_value(self):
-        return self._fill_value
-
-    @fill_value.setter
-    def fill_value(self, fill_value):
-        if fill_value is not None:
-            # Convert the given value to the dtype of the data manager.
-            fill_value = np.asarray([fill_value])[0]
-            target_dtype = self.dtype
-            if fill_value.dtype.kind == 'f' and target_dtype.kind in 'biu':
-                # Perform rounding when converting floats to ints.
-                fill_value = np.rint(fill_value)
-            try:
-                [fill_value] = np.asarray([fill_value], dtype=target_dtype)
-            except OverflowError:
-                emsg = 'Fill value of {!r} invalid for {!r}.'
-                raise ValueError(emsg.format(fill_value, self.dtype))
-        self._fill_value = fill_value
+        return self.core_data().dtype
 
     @property
     def ndim(self):
@@ -476,7 +300,7 @@ def shape(self):
         """
         return self.core_data().shape
 
-    def copy(self, data=None, fill_value='none', realised_dtype='none'):
+    def copy(self, data=None):
         """
         Returns a deep copy of this :class:`~iris._data_manager.DataManager`
         instance.
@@ -486,20 +310,12 @@ def copy(self, data=None, fill_value='none', realised_dtype='none'):
         * data:
             Replace the data of the copy with this data.
 
-        * fill_value:
-            Replacement fill-value.
-
-        * realised_dtype:
-            Replace the intended dtype of the lazy data
-            in the copy with this :class:`~numpy.dtype`.
-
         Returns:
             A copy :class:`~iris._data_manager.DataManager` instance.
 
         """
         memo = {}
-        return self._deepcopy(memo, data=data, fill_value=fill_value,
-                              realised_dtype=realised_dtype)
+        return self._deepcopy(memo, data=data)
 
     def core_data(self):
         """
@@ -548,45 +364,3 @@ def lazy_data(self):
             result = as_lazy_data(self._real_array)
 
         return result
-
-    def replace(self, data, fill_value=None, realised_dtype=None):
-        """
-        Perform an in-place replacement of the managed data.
-
-        Args:
-
-        * data:
-            Replace the managed data with either the :class:`~numpy.ndarray`
-            or :class:`~numpy.ma.core.MaskedArray` real data, or lazy
-            :class:`dask.array.core.Array`
-
-        Kwargs:
-
-        * fill_value:
-            Replacement for the :class:`~iris._data_manager.DataManager`
-            fill-value.
-
-        * realised_dtype:
-            The intended dtype of the specified lazy data.
-
-        .. note::
-            Data replacement alone will clear the intended dtype
-            of the realised lazy data, and the fill-value.
-
-        """
-        # Snapshot the currently managed data.
-        original_data = self.core_data()
-        # Perform in-place data assignment.
-        self.data = data
-        try:
-            self._realised_dtype_setter(realised_dtype)
-            self.fill_value = fill_value
-        except ValueError as error:
-            # Backout the data replacement, and reinstate the cached
-            # original managed data.
-            self._lazy_array = self._real_array = None
-            if is_lazy_data(original_data):
-                self._lazy_array = original_data
-            else:
-                self._real_array = original_data
-            raise error
diff --git a/lib/iris/_lazy_data.py b/lib/iris/_lazy_data.py
index 5fb61b81f3..985e79af13 100644
--- a/lib/iris/_lazy_data.py
+++ b/lib/iris/_lazy_data.py
@@ -94,13 +94,12 @@ def as_lazy_data(data, chunks=_MAX_CHUNK_SIZE):
 
     """
     if not is_lazy_data(data):
-        if ma.isMaskedArray(data):
-            data = array_masked_to_nans(data)
-        data = da.from_array(data, chunks=chunks)
+        asarray = not ma.isMaskedArray(data)
+        data = da.from_array(data, chunks=chunks, asarray=asarray)
     return data
 
 
-def as_concrete_data(data, **kwargs):
+def as_concrete_data(data):
     """
     Return the actual content of a lazy array, as a numpy array.
     If the input data is a NumPy `ndarray` or masked array, return it
@@ -108,17 +107,11 @@ def as_concrete_data(data, **kwargs):
 
     If the input data is lazy, return the realised result.
 
-    Where lazy data contains NaNs these are translated by filling or converting
-    to masked data, using the :func:`~iris._lazy_data.convert_nans_array`
-    function.
-
     Args:
 
     * data:
         A dask array, NumPy `ndarray` or masked array
 
-    Kwargs are passed through to :func:`~iris._lazy_data.convert_nans_array`.
-
     Returns:
         A NumPy `ndarray` or masked array.
 
@@ -129,53 +122,10 @@ def as_concrete_data(data, **kwargs):
         # rather than a numpy.ndarray object.
         # Recorded in https://github.com/dask/dask/issues/2111.
         data = np.asanyarray(data.compute())
-        # Convert any missing data as requested.
-        data = convert_nans_array(data, **kwargs)
 
     return data
 
 
-def nan_array_type(dtype):
-    return np.dtype('f8') if dtype.kind in 'biu' else dtype
-
-
-def array_masked_to_nans(array):
-    """
-    Convert a masked array to a NumPy `ndarray` filled with NaN values. Input
-    NumPy arrays with no mask are returned unchanged.
-    This is used for dask integration, as dask does not support masked arrays.
-
-    Args:
-
-    * array:
-        A NumPy `ndarray` or masked array.
-
-    Returns:
-        A NumPy `ndarray`. This is the input array if unmasked, or an array
-        of floating-point values with NaN values where the mask was `True` if
-        the input array is masked.
-
-    .. note::
-        The fill value and mask of the input masked array will be lost.
-
-    .. note::
-        Integer masked arrays are cast to 8-byte floats because NaN is a
-        floating-point value.
-
-    """
-    if not ma.isMaskedArray(array):
-        result = array
-    else:
-        if ma.is_masked(array):
-            mask = array.mask
-            new_dtype = nan_array_type(array.data.dtype)
-            result = array.data.astype(new_dtype)
-            result[mask] = np.nan
-        else:
-            result = array.data
-    return result
-
-
 def multidim_lazy_stack(stack):
     """
     Recursively build a multidimensional stacked dask array.
@@ -202,70 +152,3 @@ def multidim_lazy_stack(stack):
         result = da.stack([multidim_lazy_stack(subarray)
                            for subarray in stack])
     return result
-
-
-def convert_nans_array(array, nans_replacement=None, result_dtype=None):
-    """
-    Convert a :class:`~numpy.ndarray` that may contain one or more NaN values
-    to either a :class:`~numpy.ma.core.MaskedArray` or a
-    :class:`~numpy.ndarray` with the NaN values filled.
-
-    Args:
-
-    * array:
-        The :class:`~numpy.ndarray` to be converted.
-
-    Kwargs:
-
-    * nans_replacement:
-        If `nans_replacement` is None, then raise an exception if the `array`
-        contains any NaN values (default behaviour).
-        If `nans_replacement` is `numpy.ma.masked`, then convert the `array`
-        to a :class:`~numpy.ma.core.MaskedArray`.
-        Otherwise, use the specified `nans_replacement` value as the `array`
-        fill value.
-
-    * result_dtype:
-        Cast the resultant array to this target :class:`~numpy.dtype`.
-
-    Returns:
-        An :class:`numpy.ndarray`.
-
-    .. note::
-        An input array that is either a :class:`~numpy.ma.core.MaskedArray`
-        or has an integral dtype will be returned unaltered.
-
-    .. note::
-        In some cases, the input array is modified in-place.
-
-    """
-    if not ma.isMaskedArray(array) and array.dtype.kind == 'f':
-        # First, calculate the mask.
-        mask = np.isnan(array)
-        # Now, cast the dtype, if required.
-        if result_dtype is not None:
-            result_dtype = np.dtype(result_dtype)
-            if array.dtype != result_dtype:
-                array = array.astype(result_dtype)
-        # Finally, mask or fill the data, as required or raise an exception
-        # if we detect there are NaNs present and we didn't expect any.
-        if np.any(mask):
-            if nans_replacement is None:
-                emsg = 'Array contains unexpected NaNs.'
-                raise ValueError(emsg)
-            elif nans_replacement is ma.masked:
-                # Mask the array with the default fill_value.
-                array = ma.masked_array(array, mask=mask)
-            else:
-                # Check the fill value is appropriate for the
-                # result array dtype.
-                try:
-                    [fill_value] = np.asarray([nans_replacement],
-                                              dtype=array.dtype)
-                except OverflowError:
-                    emsg = 'Fill value of {!r} invalid for array result {!r}.'
-                    raise ValueError(emsg.format(nans_replacement,
-                                                 array.dtype))
-                # Fill the array.
-                array[mask] = fill_value
-    return array
diff --git a/lib/iris/_merge.py b/lib/iris/_merge.py
index 754bee7b86..ee87cefe82 100644
--- a/lib/iris/_merge.py
+++ b/lib/iris/_merge.py
@@ -315,7 +315,7 @@ class _CoordSignature(namedtuple('CoordSignature',
 
 class _CubeSignature(namedtuple('CubeSignature',
                                 ['defn', 'data_shape', 'data_type',
-                                 'fill_value', 'cell_measures_and_dims'])):
+                                 'cell_measures_and_dims'])):
     """
     Criterion for identifying a specific type of :class:`iris.cube.Cube`
     based on its metadata.
@@ -331,9 +331,6 @@ class _CubeSignature(namedtuple('CubeSignature',
     * data_type:
         The data payload :class:`numpy.dtype` of a :class:`iris.cube.Cube`.
 
-    * fill_value:
-        The fill-value for the data payload of a :class:`iris.cube.Cube`.
-
     * cell_measures_and_dims:
         A list of cell_measures and dims for the cube.
 
@@ -1241,9 +1238,7 @@ def merge(self, unique=True):
                 # All inputs were concrete, so turn the result back into a
                 # normal array.
                 dtype = self._cube_signature.data_type
-                merged_data = as_concrete_data(merged_data,
-                                               nans_replacement=ma.masked,
-                                               result_dtype=dtype)
+                merged_data = as_concrete_data(merged_data)
                 # Unmask the array if it has no masked points.
                 if (ma.isMaskedArray(merged_data) and
                         not ma.is_masked(merged_data)):
@@ -1283,14 +1278,6 @@ def register(self, cube, error_on_mismatch=False):
         other = self._build_signature(cube)
         match = cube_signature.match(other, error_on_mismatch)
         if match:
-            # Determine whether the fill value requires to be demoted
-            # to the default value.
-            if cube_signature.fill_value is not None:
-                if cube_signature.fill_value != other.fill_value:
-                    # Demote the fill value to the default.
-                    signature = self._build_signature(self._source,
-                                                      default_fill_value=True)
-                    self._cube_signature = signature
             coord_payload = self._extract_coord_payload(cube)
             match = coord_payload.match_signature(self._coord_signature,
                                                   error_on_mismatch)
@@ -1504,8 +1491,6 @@ def _get_cube(self, data):
                               dim_coords_and_dims=dim_coords_and_dims,
                               aux_coords_and_dims=aux_coords_and_dims,
                               cell_measures_and_dims=cms_and_dims,
-                              fill_value=signature.fill_value,
-                              dtype=signature.data_type,
                               **kwargs)
 
         # Add on any aux coord factories.
@@ -1611,7 +1596,7 @@ def _build_coordinates(self):
                               self._vector_aux_coords_dims):
             aux_coords_and_dims.append(_CoordAndDims(item.coord, dims))
 
-    def _build_signature(self, cube, default_fill_value=False):
+    def _build_signature(self, cube):
         """
         Generate the signature that defines this cube.
 
@@ -1620,22 +1605,13 @@ def _build_signature(self, cube, default_fill_value=False):
         * cube:
             The source cube to create the cube signature from.
 
-        Kwargs:
-
-        * default_fill_value:
-            Override the cube fill value with the default fill value of None.
-            Default is False i.e. use the provided cube.fill_value when
-            constructing the cube signature.
-
         Returns:
             The cube signature.
 
         """
-        fill_value = cube.fill_value
-        if default_fill_value:
-            fill_value = None
-        return _CubeSignature(cube.metadata, cube.shape, cube.dtype,
-                              fill_value, cube._cell_measures_and_dims)
+
+        return _CubeSignature(cube.metadata, cube.shape,
+                              cube.dtype, cube._cell_measures_and_dims)
 
     def _add_cube(self, cube, coord_payload):
         """Create and add the source-cube skeleton to the ProtoCube."""
diff --git a/lib/iris/analysis/__init__.py b/lib/iris/analysis/__init__.py
index 818bf2ac91..74bce2a458 100644
--- a/lib/iris/analysis/__init__.py
+++ b/lib/iris/analysis/__init__.py
@@ -563,8 +563,7 @@ def post_process(self, collapsed_cube, data_result, coords, **kwargs):
             The collapsed cube with its aggregated data payload.
 
         """
-        collapsed_cube.replace(data_result,
-                               fill_value=collapsed_cube.fill_value)
+        collapsed_cube.data = data_result
         return collapsed_cube
 
     def aggregate_shape(self, **kwargs):
diff --git a/lib/iris/analysis/_interpolate_private.py b/lib/iris/analysis/_interpolate_private.py
index a56683f8c2..3990fb6414 100644
--- a/lib/iris/analysis/_interpolate_private.py
+++ b/lib/iris/analysis/_interpolate_private.py
@@ -602,7 +602,6 @@ def regrid(source_cube, grid_cube, mode='bilinear', **kwargs):
     # Start with just the metadata and the re-sampled data...
     new_cube = iris.cube.Cube(new_data)
     new_cube.metadata = source_cube.metadata
-    new_cube.fill_value = source_cube.fill_value
 
     # ... and then copy across all the unaffected coordinates.
 
diff --git a/lib/iris/analysis/_interpolation.py b/lib/iris/analysis/_interpolation.py
index 46dd1115b6..405a14e24e 100644
--- a/lib/iris/analysis/_interpolation.py
+++ b/lib/iris/analysis/_interpolation.py
@@ -627,7 +627,6 @@ def __call__(self, sample_points, collapse_scalar=True):
         cube = self._src_cube
         new_cube = iris.cube.Cube(interpolated_data)
         new_cube.metadata = cube.metadata
-        new_cube.fill_value = cube.fill_value
 
         def construct_new_coord_given_points(coord, points):
             # Handle what was previously a DimCoord which may no longer be
diff --git a/lib/iris/analysis/_regrid.py b/lib/iris/analysis/_regrid.py
index 8dfffc0c2e..eb7a16d075 100644
--- a/lib/iris/analysis/_regrid.py
+++ b/lib/iris/analysis/_regrid.py
@@ -391,7 +391,6 @@ def _create_cube(data, src, x_dim, y_dim, src_x_coord, src_y_coord,
         # Create a result cube with the appropriate metadata
         result = iris.cube.Cube(data)
         result.metadata = copy.deepcopy(src.metadata)
-        result.fill_value = src.fill_value
 
         # Copy across all the coordinates which don't span the grid.
         # Record a mapping from old coordinate IDs to new coordinates,
diff --git a/lib/iris/analysis/calculus.py b/lib/iris/analysis/calculus.py
index 8d7d35d9c4..a18a4a2aed 100644
--- a/lib/iris/analysis/calculus.py
+++ b/lib/iris/analysis/calculus.py
@@ -341,9 +341,8 @@ def _copy_cube_transformed(src_cube, data, coord_func):
     assert src_cube.ndim == data.ndim
 
     # Start with just the metadata and the data...
-    new_cube = iris.cube.Cube(data,
-                              fill_value=src_cube.fill_value,
-                              dtype=src_cube.dtype)
+    new_cube = iris.cube.Cube(data)
+    new_cube.metadata = src_cube.metadata
     new_cube.metadata = src_cube.metadata
 
     # ... and then create all the coordinates.
diff --git a/lib/iris/analysis/cartography.py b/lib/iris/analysis/cartography.py
index 481350b39d..2f61cb7f37 100644
--- a/lib/iris/analysis/cartography.py
+++ b/lib/iris/analysis/cartography.py
@@ -765,7 +765,6 @@ def project(cube, target_proj, nx=None, ny=None):
 
     # Copy metadata across
     new_cube.metadata = cube.metadata
-    new_cube.fill_value = cube.fill_value
 
     return new_cube, extent
 
diff --git a/lib/iris/analysis/trajectory.py b/lib/iris/analysis/trajectory.py
index 7ca49f0e7b..c5433c91fc 100644
--- a/lib/iris/analysis/trajectory.py
+++ b/lib/iris/analysis/trajectory.py
@@ -380,9 +380,6 @@ def interpolate(cube, sample_points, method=None):
             new_cube_coord.points = src_coord.points[fancy_coord_index_arrays]
             # NOTE: the new coords do *not* have bounds.
 
-    # Set the fill-value last, as any previous data setter will clear it.
-    new_cube.fill_value = cube.fill_value
-
     return new_cube
 
 
@@ -547,7 +544,6 @@ def __call__(self, src_cube):
         # Make a new result cube with the reshaped data.
         result_cube = iris.cube.Cube(data_2d_x_and_y)
         result_cube.metadata = src_cube.metadata
-        result_cube.fill_value = src_cube.fill_value
 
         # Copy all the coords from the trajectory result.
         i_trajectory_dim = result_trajectory_cube.ndim - 1
diff --git a/lib/iris/coords.py b/lib/iris/coords.py
index e2cc855de2..d651770c6e 100644
--- a/lib/iris/coords.py
+++ b/lib/iris/coords.py
@@ -1866,12 +1866,7 @@ def data(self, data):
             raise ValueError('The data payload of a CellMeasure may not be '
                              'None; it must be a numpy array or equivalent.')
         if is_lazy_data(data) and data.dtype.kind in 'biu':
-            # Disallow lazy integral data, as it will cause problems with dask
-            # if it turns out to contain any masked points.
-            # Non-floating cell measures are not valid up to CF v1.7 anyway,
-            # but this avoids any possible problems with non-compliant files.
-            # Future usage could be supported by adding a fill_value and dtype
-            # as for cube data.  For now, disallowing it is just simpler.
+            # Non-floating cell measures are not valid up to CF v1.7
             msg = ('Cannot create cell measure with lazy data of type {}, as '
                    'integer types are not currently supported.')
             raise ValueError(msg.format(data.dtype))
diff --git a/lib/iris/cube.py b/lib/iris/cube.py
index efa8d4a34d..2bd02424c1 100644
--- a/lib/iris/cube.py
+++ b/lib/iris/cube.py
@@ -41,7 +41,6 @@
 import iris._concatenate
 import iris._constraints
 from iris._data_manager import DataManager
-from iris._deprecation import warn_deprecated
 
 import iris._merge
 import iris.analysis
@@ -648,7 +647,7 @@ def __init__(self, data, standard_name=None, long_name=None,
                  var_name=None, units=None, attributes=None,
                  cell_methods=None, dim_coords_and_dims=None,
                  aux_coords_and_dims=None, aux_factories=None,
-                 cell_measures_and_dims=None, fill_value=None, dtype=None):
+                 cell_measures_and_dims=None):
         """
         Creates a cube with data and optional metadata.
 
@@ -695,14 +694,6 @@ def __init__(self, data, standard_name=None, long_name=None,
             :mod:`iris.aux_factory`.
         * cell_measures_and_dims
             A list of CellMeasures with dimension mappings.
-        * fill_value
-            The intended fill-value of :class:`~iris.cube.Cube` masked data.
-            Note that, the fill-value is cast relative to the dtype of the
-            :class:`~iris.cube.Cube`.
-        * dtype
-            The intended dtype of the specified lazy data, which must be
-            either integer or boolean. This is to handle the case of lazy
-            integer or boolean masked data.
 
         For example::
             >>> from iris.coords import DimCoord
@@ -723,8 +714,7 @@ def __init__(self, data, standard_name=None, long_name=None,
             raise TypeError('Invalid data type: {!r}.'.format(data))
 
         # Initialise the cube data manager.
-        self._data_manager = DataManager(data, fill_value=fill_value,
-                                         realised_dtype=dtype)
+        self._data_manager = DataManager(data)
 
         #: The "standard name" for the Cube's phenomenon.
         self.standard_name = standard_name
@@ -1589,27 +1579,6 @@ def dtype(self):
         """
         return self._data_manager.dtype
 
-    @property
-    def fill_value(self):
-        """
-        A fill value for the data of the :class:`~iris.cube.Cube`.
-
-        This is a value suitable for filling masked points in this cube's data.
-        It may be ``None``, meaning that no suitable fill value is known.
-
-        .. Note::
-
-            Ideally, this value will not occur anywhere in the cube data.
-            Thus, many operations that change cube data will also set
-            ``fill_value`` to ``None``.
-
-        """
-        return self._data_manager.fill_value
-
-    @fill_value.setter
-    def fill_value(self, fill_value):
-        self._data_manager.fill_value = fill_value
-
     @property
     def ndim(self):
         """The number of dimensions in the data of this cube."""
@@ -2146,9 +2115,7 @@ def new_cell_measure_dims(cm_):
             data = ma.array(data.data, mask=data.mask, dtype=cube_data.dtype)
 
         # Make the new cube slice
-        cube = Cube(data,
-                    fill_value=self.fill_value,
-                    dtype=self._data_manager.dtype)
+        cube = Cube(data)
         cube.metadata = deepcopy(self.metadata)
 
         # Record a mapping from old coordinate IDs to new coordinates,
@@ -2386,9 +2353,7 @@ def make_chunk(key):
                 module = ma if ma.isMaskedArray(self.data) else np
                 func = module.concatenate
             data = func(chunk_data, dim)
-            result = iris.cube.Cube(data,
-                                    fill_value=self.fill_value,
-                                    dtype=self.dtype)
+            result = iris.cube.Cube(data)
             result.metadata = deepcopy(self.metadata)
 
             # Record a mapping from old coordinate IDs to new coordinates,
@@ -2778,8 +2743,7 @@ def transpose(self, new_order=None):
         # Transpose the data payload.
         dm = self._data_manager
         data = dm.core_data().transpose(new_order)
-        self._data_manager = DataManager(data, fill_value=dm.fill_value,
-                                         realised_dtype=dm.dtype)
+        self._data_manager = DataManager(data)
 
         dim_mapping = {src: dest for dest, src in enumerate(new_order)}
 
@@ -2821,8 +2785,6 @@ def _xml_element(self, doc, checksum=False, order=True, byteorder=True):
         if self.var_name:
             cube_xml_element.setAttribute('var_name', self.var_name)
         cube_xml_element.setAttribute('units', str(self.units))
-        if self.fill_value is not None:
-            cube_xml_element.setAttribute('fill_value', str(self.fill_value))
         cube_xml_element.setAttribute('dtype', self.dtype.name)
         cube_xml_element.setAttribute('core-dtype',
                                       self.core_data().dtype.name)
@@ -2939,40 +2901,15 @@ def _order(array):
             if order and ma.isMaskedArray(data):
                 data_xml_element.setAttribute('mask_order',
                                               _order(data.mask))
-        else:
-            dtype = self.lazy_data().dtype
-        data_xml_element.setAttribute('dtype', dtype.name)
+            else:
+                dtype = self.lazy_data().dtype
+            data_xml_element.setAttribute('dtype', dtype.name)
 
         cube_xml_element.appendChild(data_xml_element)
 
         return cube_xml_element
 
-    def replace(self, data, dtype=None, fill_value=None):
-        """
-        Perform an in-place replacement of the cube data.
-
-        Args:
-
-        * data:
-            Replace the data of the cube with the provided data payload.
-
-        Kwargs:
-
-        * dtype:
-            Replacement for the intended dtype of the realised lazy data.
-
-        * fill_value:
-            Replacement for the cube data fill-value.
-
-        .. note::
-            Data replacement alone will clear the intended dtype
-            of the realised lazy data and the fill-value.
-
-        """
-        self._data_manager.replace(data, fill_value=fill_value,
-                                   realised_dtype=dtype)
-
-    def copy(self, data=None, dtype='none', fill_value='none'):
+    def copy(self, data=None):
         """
         Returns a deep copy of this cube.
 
@@ -2981,19 +2918,12 @@ def copy(self, data=None, dtype='none', fill_value='none'):
         * data:
             Replace the data of the cube copy with provided data payload.
 
-        * dtype:
-            Replacement for the intended dtype of the realised lazy data.
-
-        * fill_value:
-            Replacement fill-value.
-
         Returns:
             A copy instance of the :class:`Cube`.
 
         """
         memo = {}
-        cube = self._deepcopy(memo, data=data, dtype=dtype,
-                              fill_value=fill_value)
+        cube = self._deepcopy(memo, data=data)
         return cube
 
     def __copy__(self):
@@ -3004,9 +2934,8 @@ def __copy__(self):
     def __deepcopy__(self, memo):
         return self._deepcopy(memo)
 
-    def _deepcopy(self, memo, data=None, dtype='none', fill_value='none'):
-        dm = self._data_manager.copy(data=data, fill_value=fill_value,
-                                     realised_dtype=dtype)
+    def _deepcopy(self, memo, data=None):
+        dm = self._data_manager.copy(data=data)
 
         new_dim_coords_and_dims = deepcopy(self._dim_coords_and_dims, memo)
         new_aux_coords_and_dims = deepcopy(self._aux_coords_and_dims, memo)
@@ -3025,9 +2954,7 @@ def _deepcopy(self, memo, data=None, dtype='none', fill_value='none'):
 
         new_cube = Cube(dm.core_data(),
                         dim_coords_and_dims=new_dim_coords_and_dims,
-                        aux_coords_and_dims=new_aux_coords_and_dims,
-                        fill_value=dm.fill_value,
-                        dtype=dm.dtype)
+                        aux_coords_and_dims=new_aux_coords_and_dims)
 
         new_cube.metadata = deepcopy(self.metadata, memo)
 
@@ -3043,10 +2970,6 @@ def __eq__(self, other):
         if isinstance(other, Cube):
             result = self.metadata == other.metadata
 
-            # check the cube fill-value.
-            if result:
-                result = self.fill_value == other.fill_value
-
             # having checked the metadata, now check the coordinates
             if result:
                 coord_comparison = iris.analysis.coord_comparison(self, other)
diff --git a/lib/iris/etc/pp_save_rules.txt b/lib/iris/etc/pp_save_rules.txt
index 8d3183729e..4d02a8babd 100644
--- a/lib/iris/etc/pp_save_rules.txt
+++ b/lib/iris/etc/pp_save_rules.txt
@@ -761,14 +761,14 @@ THEN
 
 #MDI
 IF
-    cm.fill_value is not None
+    isinstance(cm.data, ma.core.MaskedArray)
 THEN
-    pp.bmdi = cm.fill_value
+    pp.bmdi = cm.data.fill_value
 
 IF
-    cm.fill_value is None
+    not isinstance(cm.data, ma.core.MaskedArray)
 THEN
-    pp.bmdi = -1e30
+pp.bmdi = -1e30
 
 
 # CFname mega rule
diff --git a/lib/iris/experimental/regrid.py b/lib/iris/experimental/regrid.py
index 021d0ce3e2..c5c67ff688 100644
--- a/lib/iris/experimental/regrid.py
+++ b/lib/iris/experimental/regrid.py
@@ -1131,7 +1131,6 @@ def _regrid_weighted_curvilinear_to_rectilinear__perform(
     cube = iris.cube.Cube(weighted_mean.reshape(grid_cube.shape),
                           dim_coords_and_dims=dim_coords_and_dims)
     cube.metadata = copy.deepcopy(src_cube.metadata)
-    cube.fill_value = src_cube.fill_value
 
     for coord in src_cube.coords(dimensions=()):
         cube.add_aux_coord(coord.copy())
@@ -1494,7 +1493,6 @@ def _create_cube(self, data, src, src_xy_dim, src_x_coord, src_y_coord,
         # Create a result cube with the appropriate metadata
         result = iris.cube.Cube(data)
         result.metadata = copy.deepcopy(src.metadata)
-        result.fill_value = src.fill_value
 
         # Copy across all the coordinates which don't span the grid.
         # Record a mapping from old coordinate IDs to new coordinates,
diff --git a/lib/iris/fileformats/grib/__init__.py b/lib/iris/fileformats/grib/__init__.py
index 34ce13ac36..d4ea3d86af 100644
--- a/lib/iris/fileformats/grib/__init__.py
+++ b/lib/iris/fileformats/grib/__init__.py
@@ -34,7 +34,7 @@
 import numpy as np
 import numpy.ma as ma
 
-from iris._lazy_data import as_lazy_data, convert_nans_array
+from iris._lazy_data import as_lazy_data
 import iris.coord_systems as coord_systems
 from iris.exceptions import TranslationError, NotYetImplementedError
 # NOTE: careful here, to avoid circular imports (as iris imports grib)
@@ -139,7 +139,6 @@ class GribWrapper(object):
     def __init__(self, grib_message, grib_fh=None):
         """Store the grib message and compute our extra keys."""
         self.grib_message = grib_message
-        self.realised_dtype = np.array([0.]).dtype
 
         if self.edition != 1:
             emsg = 'GRIB edition {} is not supported by {!r}.'
@@ -178,14 +177,11 @@ def __init__(self, grib_message, grib_fh=None):
             # The byte offset requires to be reset back to the first byte
             # of this message. The file pointer offset is always at the end
             # of the current message due to the grib-api reading the message.
-            proxy = GribDataProxy(shape, self.realised_dtype, grib_fh.name,
+            proxy = GribDataProxy(shape, np.array([0.]).dtype, grib_fh.name,
                                   offset - message_length)
             self._data = as_lazy_data(proxy)
         else:
             values_array = _message_values(grib_message, shape)
-            # mask where the values are nan
-            self.data = convert_nans_array(values_array,
-                                           nans_replacement=ma.masked)
 
     def _confirm_in_scope(self):
         """Ensure we have a grib flavour that we choose to support."""
@@ -692,6 +688,10 @@ def _message_values(grib_message, shape):
     data = gribapi.grib_get_double_array(grib_message, 'values')
     data = data.reshape(shape)
 
+    # Handle missing values in a sensible way.
+    mask = np.isnan(data)
+    if mask.any():
+        data = ma.array(data, mask=mask, fill_value=np.nan)
     return data
 
 
diff --git a/lib/iris/fileformats/grib/_save_rules.py b/lib/iris/fileformats/grib/_save_rules.py
index 7a5a8fce49..8182246305 100644
--- a/lib/iris/fileformats/grib/_save_rules.py
+++ b/lib/iris/fileformats/grib/_save_rules.py
@@ -1160,17 +1160,20 @@ def product_definition_section(cube, grib):
 def data_section(cube, grib):
     # Masked data?
     if ma.isMaskedArray(cube.data):
-        fill_value = cube.fill_value
-        if fill_value is None or np.isnan(cube.fill_value):
+        if not np.isnan(cube.data.fill_value):
+            # Use the data's fill value.
+            fill_value = float(cube.data.fill_value)
+        else:
             # We can't use the cube's fill value if it's NaN,
             # the GRIB API doesn't like it.
             # Calculate an MDI outside the data range.
             min, max = cube.data.min(), cube.data.max()
             fill_value = min - (max - min) * 0.1
+        # Prepare the unmaksed data array, using fill_value as the MDI.
+        data = cube.data.filled(fill_value)
     else:
         fill_value = None
-
-    data = cube.data
+        data = cube.data
 
     # units scaling
     grib2_info = gptx.cf_phenom_to_grib2_info(cube.standard_name,
diff --git a/lib/iris/fileformats/grib/message.py b/lib/iris/fileformats/grib/message.py
index c936fe6e8b..d7ed3c40a6 100644
--- a/lib/iris/fileformats/grib/message.py
+++ b/lib/iris/fileformats/grib/message.py
@@ -30,7 +30,7 @@
 import numpy as np
 import numpy.ma as ma
 
-from iris._lazy_data import array_masked_to_nans, as_lazy_data
+from iris._lazy_data import as_lazy_data
 from iris.exceptions import TranslationError
 
 
@@ -120,10 +120,6 @@ def bmdi(self):
         # Default for fill value is None.
         return None
 
-    @property
-    def realised_dtype(self):
-        return np.dtype('f8')
-
     def core_data(self):
         return self.data
 
@@ -164,8 +160,7 @@ def data(self):
                 shape = (grid_section['numberOfDataPoints'],)
             else:
                 shape = (grid_section['Nj'], grid_section['Ni'])
-            proxy = _DataProxy(shape, self.realised_dtype, np.nan,
-                               self._recreate_raw)
+            proxy = _DataProxy(shape, np.dtype('f8'), self._recreate_raw)
             data = as_lazy_data(proxy)
         else:
             fmt = 'Grid definition template {} is not supported'
@@ -196,7 +191,7 @@ class _DataProxy(object):
 
     __slots__ = ('shape', 'dtype', 'recreate_raw')
 
-    def __init__(self, shape, dtype, fill_value, recreate_raw):
+    def __init__(self, shape, dtype, recreate_raw):
         self.shape = shape
         self.dtype = dtype
         self.recreate_raw = recreate_raw
@@ -258,10 +253,9 @@ def __getitem__(self, keys):
                 # Only the non-masked values are included in codedValues.
                 _data = np.empty(shape=bitmap.shape)
                 _data[bitmap.astype(bool)] = data
-                # Use nan where input = 1, the opposite of the behaviour
-                # specified by the GRIB spec.
-                _data[np.logical_not(bitmap.astype(bool))] = np.nan
-                data = _data
+                # `ma.masked_array` masks where input = 1, the opposite of
+                # the behaviour specified by the GRIB spec.
+                data = ma.masked_array(_data, mask=np.logical_not(bitmap))
             else:
                 msg = 'Shapes of data and bitmap do not match.'
                 raise TranslationError(msg)
@@ -272,7 +266,8 @@ def __getitem__(self, keys):
 
     def __repr__(self):
         msg = '<{self.__class__.__name__} shape={self.shape} ' \
-              'dtype={self.dtype!r} recreate_raw={self.recreate_raw!r} '
+              'dtype={self.dtype!r} fill_value={self.fill_value!r} ' \
+              'recreate_raw={self.recreate_raw!r} '
         return msg.format(self=self)
 
     def __getstate__(self):
diff --git a/lib/iris/fileformats/netcdf.py b/lib/iris/fileformats/netcdf.py
index deb6a26b73..e65b90ef2f 100644
--- a/lib/iris/fileformats/netcdf.py
+++ b/lib/iris/fileformats/netcdf.py
@@ -56,8 +56,7 @@
 import iris.fileformats._pyke_rules
 import iris.io
 import iris.util
-from iris._lazy_data import (array_masked_to_nans, as_lazy_data,
-                             convert_nans_array, nan_array_type)
+from iris._lazy_data import as_lazy_data
 
 # Show Pyke inference engine statistics.
 DEBUG = False
@@ -395,14 +394,7 @@ def __getitem__(self, keys):
             var = variable[keys]
         finally:
             dataset.close()
-        if ma.isMaskedArray(var):
-            if self.dtype.kind in 'biu':
-                msg = "NetCDF variable {!r} has masked data, which is not " \
-                      "supported for declared dtype {!r}."
-                raise TypeError(
-                    msg.format(self.variable_name, self.dtype.name))
-            var = array_masked_to_nans(var)
-        return np.asanyarray(var, dtype=self.dtype)
+        return np.asanyarray(var)
 
     def __repr__(self):
         fmt = '<{self.__class__.__name__} shape={self.shape}' \
@@ -510,11 +502,10 @@ def _load_cube(engine, cf, cf_var, filename):
     # Create cube with deferred data, but no metadata
     fill_value = getattr(cf_var.cf_data, '_FillValue', None)
 
-    dtype = nan_array_type(dummy_data.dtype)
-    proxy = NetCDFDataProxy(cf_var.shape, dtype,
+    proxy = NetCDFDataProxy(cf_var.shape, dummy_data.dtype,
                             filename, cf_var.cf_name, fill_value)
     data = as_lazy_data(proxy, chunks=cf_var.shape)
-    cube = iris.cube.Cube(data, fill_value=fill_value, dtype=dummy_data.dtype)
+    cube = iris.cube.Cube(data)
 
     # Reset the pyke inference engine.
     engine.reset()
@@ -1958,7 +1949,11 @@ def set_packing_ncattrs(cfvar):
             # Explicitly assign the fill_value, which will be the type default
             # in the case of an unmasked array.
             if packing is None:
-                fill_value = cube.fill_value
+                if hasattr(cube.lazy_data(), 'fill_value'):
+                    fill_value = cube.lazy_data().fill_value
+                else:
+                    fill_value = None
+
                 dtype = cube.lazy_data().dtype.newbyteorder('=')
 
             cf_var = self._dataset.createVariable(
@@ -1967,12 +1962,8 @@ def set_packing_ncattrs(cfvar):
                 **kwargs)
             set_packing_ncattrs(cf_var)
 
-            # Now stream the cube data payload straight to the netCDF
-            # data variable within the netCDF file, where any NaN values
-            # are replaced with the specified cube fill_value.
-            data = da.map_blocks(convert_nans_array, cube.lazy_data(),
-                                 nans_replacement=cube.fill_value,
-                                 result_dtype=cube.dtype)
+            data = cube.lazy_data()
+
             da.store([data], [cf_var])
 
         if cube.standard_name:
diff --git a/lib/iris/fileformats/pp.py b/lib/iris/fileformats/pp.py
index 5f79a8966e..89c374ffc7 100644
--- a/lib/iris/fileformats/pp.py
+++ b/lib/iris/fileformats/pp.py
@@ -39,8 +39,7 @@
 import netcdftime
 
 from iris._deprecation import warn_deprecated
-from iris._lazy_data import (array_masked_to_nans, as_concrete_data,
-                             as_lazy_data, is_lazy_data)
+from iris._lazy_data import as_concrete_data, as_lazy_data, is_lazy_data
 import iris.config
 import iris.fileformats.rules
 import iris.fileformats.pp_rules
@@ -862,8 +861,8 @@ def _lbpack_getter(self):
 
     @property
     def dtype(self):
-        return np.dtype('f8') if self.src_dtype.kind == 'i' \
-                 else self.src_dtype.newbyteorder('=')
+        return np.dtype('f8') if self.src_dtype.kind == 'i' else \
+            self.src_dtype.newbyteorder('=')
 
     @property
     def fill_value(self):
@@ -1081,7 +1080,7 @@ def _pp_attribute_names(header_defn):
     special_headers = list('_' + name for name in _SPECIAL_HEADERS)
     extra_data = list(EXTRA_DATA.values())
     special_attributes = ['_raw_header', 'raw_lbtim', 'raw_lbpack',
-                          'boundary_packing', '_realised_dtype']
+                          'boundary_packing']
     return normal_headers + special_headers + extra_data + special_attributes
 
 
@@ -1114,7 +1113,6 @@ def __init__(self, header=None):
         self.raw_lbtim = None
         self.raw_lbpack = None
         self.boundary_packing = None
-        self._realised_dtype = None
         if header is not None:
             self.raw_lbtim = header[self.HEADER_DICT['lbtim'][0]]
             self.raw_lbpack = header[self.HEADER_DICT['lbpack'][0]]
@@ -1286,9 +1284,7 @@ def data(self):
         """
         if is_lazy_data(self._data):
             # Replace with real data on the first access.
-            self._data = as_concrete_data(self._data,
-                                          nans_replacement=ma.masked,
-                                          result_dtype=self.realised_dtype)
+            self._data = as_concrete_data(self._data)
         return self._data
 
     @data.setter
@@ -1298,16 +1294,6 @@ def data(self, value):
     def core_data(self):
         return self._data
 
-    @property
-    def realised_dtype(self):
-        return self._data.dtype \
-            if self._realised_dtype is None \
-            else self._realised_dtype
-
-    @realised_dtype.setter
-    def realised_dtype(self, value):
-        self._realised_dtype = value
-
     @property
     def calendar(self):
         """Return the calendar of the field."""
@@ -1401,8 +1387,7 @@ def save(self, file_handle):
                 # Integer or Boolean data : No masking is supported.
                 msg = 'Non-floating masked data cannot be saved to PP.'
                 raise ValueError(msg)
-            fill_value = self.bmdi
-            data = data.filled(fill_value=fill_value)
+            data = data.filled(fill_value=self.bmdi)
 
         # Make sure the data is big-endian
         if data.dtype.newbyteorder('>') != data.dtype:
@@ -1900,7 +1885,6 @@ def _create_field_data(field, data_shape, land_mask):
                             field.raw_lbpack,
                             field.boundary_packing,
                             field.bmdi, land_mask)
-        field.realised_dtype = dtype.newbyteorder('=')
         block_shape = data_shape if 0 not in data_shape else (1, 1)
         field.data = as_lazy_data(proxy, chunks=block_shape)
 
diff --git a/lib/iris/fileformats/rules.py b/lib/iris/fileformats/rules.py
index f8e003f9b7..b101604b74 100644
--- a/lib/iris/fileformats/rules.py
+++ b/lib/iris/fileformats/rules.py
@@ -898,18 +898,11 @@ def _make_cube(field, converter):
     metadata = converter(field)
 
     cube_data = field.core_data()
-    cube_dtype = field.realised_dtype
-    if cube_dtype.kind in 'biu':
-        # Don't adopt BMDI as a fill value for integer data.
-        cube_fill_value = None
-    else:
-        cube_fill_value = field.bmdi
     cube = iris.cube.Cube(cube_data,
                           attributes=metadata.attributes,
                           cell_methods=metadata.cell_methods,
                           dim_coords_and_dims=metadata.dim_coords_and_dims,
-                          aux_coords_and_dims=metadata.aux_coords_and_dims,
-                          fill_value=cube_fill_value, dtype=cube_dtype)
+                          aux_coords_and_dims=metadata.aux_coords_and_dims)
 
     # Temporary code to deal with invalid standard names in the
     # translation table.
diff --git a/lib/iris/tests/integration/test_netcdf.py b/lib/iris/tests/integration/test_netcdf.py
index 6b6871500d..4d9895d15f 100644
--- a/lib/iris/tests/integration/test_netcdf.py
+++ b/lib/iris/tests/integration/test_netcdf.py
@@ -212,7 +212,7 @@ def test_lazy_preserved_save(self):
 
     def test_lazy_mask_preserve_fill_value(self):
         data = ma.array([0, 1], mask=[False, True])
-        cube = iris.cube.Cube(data, fill_value=-1)
+        cube = iris.cube.Cube(data)
         with self.temp_filename(suffix='.nc') as filename, \
                 self.temp_filename(suffix='.nc') as other_filename:
             iris.save(cube, filename, unlimited_dimensions=[])
diff --git a/lib/iris/tests/results/COLPEX/small_colpex_theta_p_alt.cml b/lib/iris/tests/results/COLPEX/small_colpex_theta_p_alt.cml
index 03a0fe20dd..1cd1d1d53e 100644
--- a/lib/iris/tests/results/COLPEX/small_colpex_theta_p_alt.cml
+++ b/lib/iris/tests/results/COLPEX/small_colpex_theta_p_alt.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -523,7 +523,7 @@
     <cellMethods/>
     <data checksum="0x9554cc14" dtype="float32" shape="(6, 10, 83, 83)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s00i408"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1046,7 +1046,7 @@
     <cellMethods/>
     <data checksum="0xd9d57b21" dtype="float32" shape="(6, 10, 83, 83)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="surface_altitude" units="m">
+  <cube core-dtype="float32" dtype="float32" standard_name="surface_altitude" units="m">
     <attributes>
       <attribute name="STASH" value="m01s00i033"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/FF/air_temperature_1.cml b/lib/iris/tests/results/FF/air_temperature_1.cml
index 8d653c28e9..fedd074dee 100644
--- a/lib/iris/tests/results/FF/air_temperature_1.cml
+++ b/lib/iris/tests/results/FF/air_temperature_1.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/FF/air_temperature_2.cml b/lib/iris/tests/results/FF/air_temperature_2.cml
index d06ff4d286..c0bc0fff8b 100644
--- a/lib/iris/tests/results/FF/air_temperature_2.cml
+++ b/lib/iris/tests/results/FF/air_temperature_2.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/FF/soil_temperature_1.cml b/lib/iris/tests/results/FF/soil_temperature_1.cml
index 2549b1b962..e1134337ed 100644
--- a/lib/iris/tests/results/FF/soil_temperature_1.cml
+++ b/lib/iris/tests/results/FF/soil_temperature_1.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="soil_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="soil_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s08i225"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/FF/surface_altitude_1.cml b/lib/iris/tests/results/FF/surface_altitude_1.cml
index 8ec0c305da..aec7a834e3 100644
--- a/lib/iris/tests/results/FF/surface_altitude_1.cml
+++ b/lib/iris/tests/results/FF/surface_altitude_1.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="surface_altitude" units="m">
+  <cube core-dtype="float32" dtype="float32" standard_name="surface_altitude" units="m">
     <attributes>
       <attribute name="STASH" value="m01s00i033"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/abs.cml b/lib/iris/tests/results/analysis/abs.cml
index a427761d7f..9a012ca90f 100644
--- a/lib/iris/tests/results/analysis/abs.cml
+++ b/lib/iris/tests/results/analysis/abs.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float32" dtype="float32" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/addition.cml b/lib/iris/tests/results/analysis/addition.cml
index b44455cb95..f3f54ca912 100644
--- a/lib/iris/tests/results/analysis/addition.cml
+++ b/lib/iris/tests/results/analysis/addition.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float32" dtype="float32" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/addition_coord_x.cml b/lib/iris/tests/results/analysis/addition_coord_x.cml
index 507d1ccdd9..3b5c037ee5 100644
--- a/lib/iris/tests/results/analysis/addition_coord_x.cml
+++ b/lib/iris/tests/results/analysis/addition_coord_x.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1.00000001505e+30" units="K">
+  <cube core-dtype="float64" dtype="float64" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/addition_coord_y.cml b/lib/iris/tests/results/analysis/addition_coord_y.cml
index 8edf44f3a0..816c795e33 100644
--- a/lib/iris/tests/results/analysis/addition_coord_y.cml
+++ b/lib/iris/tests/results/analysis/addition_coord_y.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1.00000001505e+30" units="K">
+  <cube core-dtype="float64" dtype="float64" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/addition_different_std_name.cml b/lib/iris/tests/results/analysis/addition_different_std_name.cml
index aa7d48f976..70488b8c3d 100644
--- a/lib/iris/tests/results/analysis/addition_different_std_name.cml
+++ b/lib/iris/tests/results/analysis/addition_different_std_name.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float32" dtype="float32" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/addition_in_place.cml b/lib/iris/tests/results/analysis/addition_in_place.cml
index b44455cb95..f3f54ca912 100644
--- a/lib/iris/tests/results/analysis/addition_in_place.cml
+++ b/lib/iris/tests/results/analysis/addition_in_place.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float32" dtype="float32" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/addition_in_place_coord.cml b/lib/iris/tests/results/analysis/addition_in_place_coord.cml
index a909fd67a9..827c8019a1 100644
--- a/lib/iris/tests/results/analysis/addition_in_place_coord.cml
+++ b/lib/iris/tests/results/analysis/addition_in_place_coord.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float32" dtype="float32" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/addition_scalar.cml b/lib/iris/tests/results/analysis/addition_scalar.cml
index 6eaf5ef2bd..2ebba99227 100644
--- a/lib/iris/tests/results/analysis/addition_scalar.cml
+++ b/lib/iris/tests/results/analysis/addition_scalar.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float32" dtype="float32" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/apply_ifunc.cml b/lib/iris/tests/results/analysis/apply_ifunc.cml
index 5e93dcfb6a..805e20c259 100644
--- a/lib/iris/tests/results/analysis/apply_ifunc.cml
+++ b/lib/iris/tests/results/analysis/apply_ifunc.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" long_name="squared temperature" units="kelvin^2">
+  <cube core-dtype="float32" dtype="float32" long_name="squared temperature" units="kelvin^2">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/apply_ifunc_frompyfunc.cml b/lib/iris/tests/results/analysis/apply_ifunc_frompyfunc.cml
index 73aa603992..9292dc2d88 100644
--- a/lib/iris/tests/results/analysis/apply_ifunc_frompyfunc.cml
+++ b/lib/iris/tests/results/analysis/apply_ifunc_frompyfunc.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="object" dtype="object" fill_value="-1e+30" units="kelvin^2">
+  <cube core-dtype="object" dtype="object" units="kelvin^2">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/apply_ifunc_original.cml b/lib/iris/tests/results/analysis/apply_ifunc_original.cml
index b86e0d7c06..de5e989950 100644
--- a/lib/iris/tests/results/analysis/apply_ifunc_original.cml
+++ b/lib/iris/tests/results/analysis/apply_ifunc_original.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/apply_ufunc.cml b/lib/iris/tests/results/analysis/apply_ufunc.cml
index 5e93dcfb6a..805e20c259 100644
--- a/lib/iris/tests/results/analysis/apply_ufunc.cml
+++ b/lib/iris/tests/results/analysis/apply_ufunc.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" long_name="squared temperature" units="kelvin^2">
+  <cube core-dtype="float32" dtype="float32" long_name="squared temperature" units="kelvin^2">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/apply_ufunc_frompyfunc.cml b/lib/iris/tests/results/analysis/apply_ufunc_frompyfunc.cml
index fc7cce9134..3e7dd10957 100644
--- a/lib/iris/tests/results/analysis/apply_ufunc_frompyfunc.cml
+++ b/lib/iris/tests/results/analysis/apply_ufunc_frompyfunc.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="object" dtype="object" fill_value="-1e+30" units="unknown">
+  <cube core-dtype="object" dtype="object" units="unknown">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/apply_ufunc_original.cml b/lib/iris/tests/results/analysis/apply_ufunc_original.cml
index b86e0d7c06..de5e989950 100644
--- a/lib/iris/tests/results/analysis/apply_ufunc_original.cml
+++ b/lib/iris/tests/results/analysis/apply_ufunc_original.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/areaweights_original.cml b/lib/iris/tests/results/analysis/areaweights_original.cml
index 49f0dcf24d..f5197f9d77 100644
--- a/lib/iris/tests/results/analysis/areaweights_original.cml
+++ b/lib/iris/tests/results/analysis/areaweights_original.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="9999.0" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/division.cml b/lib/iris/tests/results/analysis/division.cml
index c91c6c4919..1210f3d736 100644
--- a/lib/iris/tests/results/analysis/division.cml
+++ b/lib/iris/tests/results/analysis/division.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="1">
+  <cube core-dtype="float32" dtype="float32" units="1">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/division_by_array.cml b/lib/iris/tests/results/analysis/division_by_array.cml
index 781f95173d..279fc00969 100644
--- a/lib/iris/tests/results/analysis/division_by_array.cml
+++ b/lib/iris/tests/results/analysis/division_by_array.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="kelvin">
+  <cube core-dtype="float32" dtype="float32" units="kelvin">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/division_by_latitude.cml b/lib/iris/tests/results/analysis/division_by_latitude.cml
index e68307ded1..a9570c2dfe 100644
--- a/lib/iris/tests/results/analysis/division_by_latitude.cml
+++ b/lib/iris/tests/results/analysis/division_by_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="57.2957795130823 kelvin-radian^-1">
+  <cube core-dtype="float32" dtype="float32" units="57.2957795130823 kelvin-radian^-1">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/division_by_longitude.cml b/lib/iris/tests/results/analysis/division_by_longitude.cml
index 31da15b10d..8f7c88d240 100644
--- a/lib/iris/tests/results/analysis/division_by_longitude.cml
+++ b/lib/iris/tests/results/analysis/division_by_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="57.2957795130823 kelvin-radian^-1">
+  <cube core-dtype="float32" dtype="float32" units="57.2957795130823 kelvin-radian^-1">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/division_by_singular_coord.cml b/lib/iris/tests/results/analysis/division_by_singular_coord.cml
index 9fc56108d5..8599423542 100644
--- a/lib/iris/tests/results/analysis/division_by_singular_coord.cml
+++ b/lib/iris/tests/results/analysis/division_by_singular_coord.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1.00000001505e+30" units="kelvin">
+  <cube core-dtype="float64" dtype="float64" units="kelvin">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/division_scalar.cml b/lib/iris/tests/results/analysis/division_scalar.cml
index 781f95173d..279fc00969 100644
--- a/lib/iris/tests/results/analysis/division_scalar.cml
+++ b/lib/iris/tests/results/analysis/division_scalar.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="kelvin">
+  <cube core-dtype="float32" dtype="float32" units="kelvin">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/exponentiate.cml b/lib/iris/tests/results/analysis/exponentiate.cml
index 62f4bf08ab..1e8db08a0f 100644
--- a/lib/iris/tests/results/analysis/exponentiate.cml
+++ b/lib/iris/tests/results/analysis/exponentiate.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1.00000001505e+30" units="kelvin^4">
+  <cube core-dtype="float64" dtype="float64" units="kelvin^4">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/gmean_latitude.cml b/lib/iris/tests/results/analysis/gmean_latitude.cml
index e71bb14e74..138073df12 100644
--- a/lib/iris/tests/results/analysis/gmean_latitude.cml
+++ b/lib/iris/tests/results/analysis/gmean_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/gmean_latitude_longitude.cml b/lib/iris/tests/results/analysis/gmean_latitude_longitude.cml
index 1176acb50c..f37d247c47 100644
--- a/lib/iris/tests/results/analysis/gmean_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/gmean_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/gmean_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/gmean_latitude_longitude_1call.cml
index ac4ed1681d..4e12d0c5f5 100644
--- a/lib/iris/tests/results/analysis/gmean_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/gmean_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/hmean_latitude.cml b/lib/iris/tests/results/analysis/hmean_latitude.cml
index 6cc2242648..806acbb4c5 100644
--- a/lib/iris/tests/results/analysis/hmean_latitude.cml
+++ b/lib/iris/tests/results/analysis/hmean_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/hmean_latitude_longitude.cml b/lib/iris/tests/results/analysis/hmean_latitude_longitude.cml
index 2abf38fef2..9b8e4169d1 100644
--- a/lib/iris/tests/results/analysis/hmean_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/hmean_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/hmean_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/hmean_latitude_longitude_1call.cml
index 931e8c0a97..923e323714 100644
--- a/lib/iris/tests/results/analysis/hmean_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/hmean_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/interpolation/linear/real_2dslice.cml b/lib/iris/tests/results/analysis/interpolation/linear/real_2dslice.cml
index 3533831071..695b038f0c 100644
--- a/lib/iris/tests/results/analysis/interpolation/linear/real_2dslice.cml
+++ b/lib/iris/tests/results/analysis/interpolation/linear/real_2dslice.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/interpolation/linear/real_2slices.cml b/lib/iris/tests/results/analysis/interpolation/linear/real_2slices.cml
index 20a59d23a9..4c5f273fa6 100644
--- a/lib/iris/tests/results/analysis/interpolation/linear/real_2slices.cml
+++ b/lib/iris/tests/results/analysis/interpolation/linear/real_2slices.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/interpolation/linear/real_circular_2dslice.cml b/lib/iris/tests/results/analysis/interpolation/linear/real_circular_2dslice.cml
index dbf4f6dbe8..b4365291b4 100644
--- a/lib/iris/tests/results/analysis/interpolation/linear/real_circular_2dslice.cml
+++ b/lib/iris/tests/results/analysis/interpolation/linear/real_circular_2dslice.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_bounded.cml b/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_bounded.cml
index 4044ad0497..f9c1138755 100644
--- a/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_bounded.cml
+++ b/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_bounded.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_bounded_mid_point.cml b/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_bounded_mid_point.cml
index 4044ad0497..f9c1138755 100644
--- a/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_bounded_mid_point.cml
+++ b/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_bounded_mid_point.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_latitude.cml b/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_latitude.cml
index a7b0953a56..7f98c24e4d 100644
--- a/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_latitude.cml
+++ b/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_latitude_longitude.cml b/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_latitude_longitude.cml
index da5633089a..31f864502f 100644
--- a/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/interpolation/nearest_neighbour_extract_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/log.cml b/lib/iris/tests/results/analysis/log.cml
index ff5147fb1e..8bbe5a3a58 100644
--- a/lib/iris/tests/results/analysis/log.cml
+++ b/lib/iris/tests/results/analysis/log.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="ln(re 1 kelvin)">
+  <cube core-dtype="float32" dtype="float32" units="ln(re 1 kelvin)">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/log10.cml b/lib/iris/tests/results/analysis/log10.cml
index e1c1bbe21b..1ef012c899 100644
--- a/lib/iris/tests/results/analysis/log10.cml
+++ b/lib/iris/tests/results/analysis/log10.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="lg(re 1 kelvin)">
+  <cube core-dtype="float32" dtype="float32" units="lg(re 1 kelvin)">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/log2.cml b/lib/iris/tests/results/analysis/log2.cml
index 30da9b3566..9d4a9b88a8 100644
--- a/lib/iris/tests/results/analysis/log2.cml
+++ b/lib/iris/tests/results/analysis/log2.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="lb(re 1 kelvin)">
+  <cube core-dtype="float32" dtype="float32" units="lb(re 1 kelvin)">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/maths_original.cml b/lib/iris/tests/results/analysis/maths_original.cml
index a1757f47e8..6c05986111 100644
--- a/lib/iris/tests/results/analysis/maths_original.cml
+++ b/lib/iris/tests/results/analysis/maths_original.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/max_latitude.cml b/lib/iris/tests/results/analysis/max_latitude.cml
index b9acb2e1a0..b60e76ea8d 100644
--- a/lib/iris/tests/results/analysis/max_latitude.cml
+++ b/lib/iris/tests/results/analysis/max_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/max_latitude_longitude.cml b/lib/iris/tests/results/analysis/max_latitude_longitude.cml
index 623d412a61..3a7d98bbb1 100644
--- a/lib/iris/tests/results/analysis/max_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/max_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/max_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/max_latitude_longitude_1call.cml
index f432a91b37..3291118177 100644
--- a/lib/iris/tests/results/analysis/max_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/max_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/mean_latitude.cml b/lib/iris/tests/results/analysis/mean_latitude.cml
index 0317e2b1e2..f7e97e1ec3 100644
--- a/lib/iris/tests/results/analysis/mean_latitude.cml
+++ b/lib/iris/tests/results/analysis/mean_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/mean_latitude_longitude.cml b/lib/iris/tests/results/analysis/mean_latitude_longitude.cml
index a45e0a610e..ed89374ee5 100644
--- a/lib/iris/tests/results/analysis/mean_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/mean_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/mean_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/mean_latitude_longitude_1call.cml
index 44f9930efd..f5caed6288 100644
--- a/lib/iris/tests/results/analysis/mean_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/mean_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/median_latitude.cml b/lib/iris/tests/results/analysis/median_latitude.cml
index b43235dd05..b5c35a765f 100644
--- a/lib/iris/tests/results/analysis/median_latitude.cml
+++ b/lib/iris/tests/results/analysis/median_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/median_latitude_longitude.cml b/lib/iris/tests/results/analysis/median_latitude_longitude.cml
index 4e1335e64b..dc4196bffd 100644
--- a/lib/iris/tests/results/analysis/median_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/median_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/median_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/median_latitude_longitude_1call.cml
index f617c0895f..f02423597d 100644
--- a/lib/iris/tests/results/analysis/median_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/median_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/min_latitude.cml b/lib/iris/tests/results/analysis/min_latitude.cml
index 7cf5ac7130..b79085ea21 100644
--- a/lib/iris/tests/results/analysis/min_latitude.cml
+++ b/lib/iris/tests/results/analysis/min_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/min_latitude_longitude.cml b/lib/iris/tests/results/analysis/min_latitude_longitude.cml
index 0f4087c17c..1889a86e0d 100644
--- a/lib/iris/tests/results/analysis/min_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/min_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/min_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/min_latitude_longitude_1call.cml
index cb6d0f200d..c93909c324 100644
--- a/lib/iris/tests/results/analysis/min_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/min_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/multiply.cml b/lib/iris/tests/results/analysis/multiply.cml
index a96908621c..9fe9f1a16b 100644
--- a/lib/iris/tests/results/analysis/multiply.cml
+++ b/lib/iris/tests/results/analysis/multiply.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="kelvin^2">
+  <cube core-dtype="float32" dtype="float32" units="kelvin^2">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/multiply_different_std_name.cml b/lib/iris/tests/results/analysis/multiply_different_std_name.cml
index 510934ba83..5d75a86e81 100644
--- a/lib/iris/tests/results/analysis/multiply_different_std_name.cml
+++ b/lib/iris/tests/results/analysis/multiply_different_std_name.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="kelvin^2">
+  <cube core-dtype="float32" dtype="float32" units="kelvin^2">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/original.cml b/lib/iris/tests/results/analysis/original.cml
index 7229c5903a..683d505487 100644
--- a/lib/iris/tests/results/analysis/original.cml
+++ b/lib/iris/tests/results/analysis/original.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/original_common.cml b/lib/iris/tests/results/analysis/original_common.cml
index 2b7643b909..d6aa8fe63b 100644
--- a/lib/iris/tests/results/analysis/original_common.cml
+++ b/lib/iris/tests/results/analysis/original_common.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/original_hmean.cml b/lib/iris/tests/results/analysis/original_hmean.cml
index f342ccc1b7..cda6275472 100644
--- a/lib/iris/tests/results/analysis/original_hmean.cml
+++ b/lib/iris/tests/results/analysis/original_hmean.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/linear_both_circular.cml b/lib/iris/tests/results/analysis/regrid/linear_both_circular.cml
index 171925699d..ef8e0217a2 100644
--- a/lib/iris/tests/results/analysis/regrid/linear_both_circular.cml
+++ b/lib/iris/tests/results/analysis/regrid/linear_both_circular.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/linear_circular_grid.cml b/lib/iris/tests/results/analysis/regrid/linear_circular_grid.cml
index 08c5a81e1f..23da537d1a 100644
--- a/lib/iris/tests/results/analysis/regrid/linear_circular_grid.cml
+++ b/lib/iris/tests/results/analysis/regrid/linear_circular_grid.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/linear_circular_src.cml b/lib/iris/tests/results/analysis/regrid/linear_circular_src.cml
index 5d832e6ba6..a39cf83d04 100644
--- a/lib/iris/tests/results/analysis/regrid/linear_circular_src.cml
+++ b/lib/iris/tests/results/analysis/regrid/linear_circular_src.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/linear_circular_srcmissingmask.cml b/lib/iris/tests/results/analysis/regrid/linear_circular_srcmissingmask.cml
index 5d832e6ba6..a39cf83d04 100644
--- a/lib/iris/tests/results/analysis/regrid/linear_circular_srcmissingmask.cml
+++ b/lib/iris/tests/results/analysis/regrid/linear_circular_srcmissingmask.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/linear_non_circular.cml b/lib/iris/tests/results/analysis/regrid/linear_non_circular.cml
index ded7ffd106..7faef54684 100644
--- a/lib/iris/tests/results/analysis/regrid/linear_non_circular.cml
+++ b/lib/iris/tests/results/analysis/regrid/linear_non_circular.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/nearest_both_circular.cml b/lib/iris/tests/results/analysis/regrid/nearest_both_circular.cml
index d14b6e1d2d..78d6a79c4a 100644
--- a/lib/iris/tests/results/analysis/regrid/nearest_both_circular.cml
+++ b/lib/iris/tests/results/analysis/regrid/nearest_both_circular.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/nearest_circular_grid.cml b/lib/iris/tests/results/analysis/regrid/nearest_circular_grid.cml
index d73639f66d..e1f6df038b 100644
--- a/lib/iris/tests/results/analysis/regrid/nearest_circular_grid.cml
+++ b/lib/iris/tests/results/analysis/regrid/nearest_circular_grid.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/nearest_circular_src.cml b/lib/iris/tests/results/analysis/regrid/nearest_circular_src.cml
index 0a589642fd..15ede8da0c 100644
--- a/lib/iris/tests/results/analysis/regrid/nearest_circular_src.cml
+++ b/lib/iris/tests/results/analysis/regrid/nearest_circular_src.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/nearest_circular_srcmissingmask.cml b/lib/iris/tests/results/analysis/regrid/nearest_circular_srcmissingmask.cml
index 0a589642fd..15ede8da0c 100644
--- a/lib/iris/tests/results/analysis/regrid/nearest_circular_srcmissingmask.cml
+++ b/lib/iris/tests/results/analysis/regrid/nearest_circular_srcmissingmask.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/regrid/nearest_non_circular.cml b/lib/iris/tests/results/analysis/regrid/nearest_non_circular.cml
index 5b842c8811..23a19b5185 100644
--- a/lib/iris/tests/results/analysis/regrid/nearest_non_circular.cml
+++ b/lib/iris/tests/results/analysis/regrid/nearest_non_circular.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/rms_latitude.cml b/lib/iris/tests/results/analysis/rms_latitude.cml
index f134bece0c..8422647cbc 100644
--- a/lib/iris/tests/results/analysis/rms_latitude.cml
+++ b/lib/iris/tests/results/analysis/rms_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/rms_latitude_longitude.cml b/lib/iris/tests/results/analysis/rms_latitude_longitude.cml
index 16fcffe176..095c9cb6ae 100644
--- a/lib/iris/tests/results/analysis/rms_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/rms_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/rms_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/rms_latitude_longitude_1call.cml
index 8c18d225bf..4fb3e44896 100644
--- a/lib/iris/tests/results/analysis/rms_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/rms_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/sqrt.cml b/lib/iris/tests/results/analysis/sqrt.cml
index fee35a10a8..e801a5e236 100644
--- a/lib/iris/tests/results/analysis/sqrt.cml
+++ b/lib/iris/tests/results/analysis/sqrt.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="kelvin">
+  <cube core-dtype="float32" dtype="float32" units="kelvin">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/std_dev_latitude.cml b/lib/iris/tests/results/analysis/std_dev_latitude.cml
index f5c5ee6634..0e3e4479ca 100644
--- a/lib/iris/tests/results/analysis/std_dev_latitude.cml
+++ b/lib/iris/tests/results/analysis/std_dev_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/std_dev_latitude_longitude.cml b/lib/iris/tests/results/analysis/std_dev_latitude_longitude.cml
index cc75ca3b56..573350d8bf 100644
--- a/lib/iris/tests/results/analysis/std_dev_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/std_dev_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/std_dev_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/std_dev_latitude_longitude_1call.cml
index 50f54f537a..f935b50cca 100644
--- a/lib/iris/tests/results/analysis/std_dev_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/std_dev_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/subtract.cml b/lib/iris/tests/results/analysis/subtract.cml
index ace9a0046d..35ef131b8f 100644
--- a/lib/iris/tests/results/analysis/subtract.cml
+++ b/lib/iris/tests/results/analysis/subtract.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float32" dtype="float32" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/subtract_array.cml b/lib/iris/tests/results/analysis/subtract_array.cml
index aa7d48f976..70488b8c3d 100644
--- a/lib/iris/tests/results/analysis/subtract_array.cml
+++ b/lib/iris/tests/results/analysis/subtract_array.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float32" dtype="float32" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/subtract_coord_x.cml b/lib/iris/tests/results/analysis/subtract_coord_x.cml
index b7665597fd..a4a9b9654d 100644
--- a/lib/iris/tests/results/analysis/subtract_coord_x.cml
+++ b/lib/iris/tests/results/analysis/subtract_coord_x.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1.00000001505e+30" units="K">
+  <cube core-dtype="float64" dtype="float64" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/subtract_coord_y.cml b/lib/iris/tests/results/analysis/subtract_coord_y.cml
index 2a9995ccab..80612ea4c3 100644
--- a/lib/iris/tests/results/analysis/subtract_coord_y.cml
+++ b/lib/iris/tests/results/analysis/subtract_coord_y.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1.00000001505e+30" units="K">
+  <cube core-dtype="float64" dtype="float64" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/subtract_scalar.cml b/lib/iris/tests/results/analysis/subtract_scalar.cml
index ff0a1ff9e2..24b360467d 100644
--- a/lib/iris/tests/results/analysis/subtract_scalar.cml
+++ b/lib/iris/tests/results/analysis/subtract_scalar.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float32" dtype="float32" units="K">
     <coords>
       <coord>
         <dimCoord bounds="[[-28083.0, 6477.0]]" id="1d45e087" points="[6477]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="int32"/>
diff --git a/lib/iris/tests/results/analysis/sum_latitude.cml b/lib/iris/tests/results/analysis/sum_latitude.cml
index 3d1e13a955..5875384cb6 100644
--- a/lib/iris/tests/results/analysis/sum_latitude.cml
+++ b/lib/iris/tests/results/analysis/sum_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/sum_latitude_longitude.cml b/lib/iris/tests/results/analysis/sum_latitude_longitude.cml
index 4135f70210..948134bea9 100644
--- a/lib/iris/tests/results/analysis/sum_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/sum_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/sum_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/sum_latitude_longitude_1call.cml
index d7f26a82f8..818f2aed1a 100644
--- a/lib/iris/tests/results/analysis/sum_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/sum_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/variance_latitude.cml b/lib/iris/tests/results/analysis/variance_latitude.cml
index 91921d0e79..60b4228404 100644
--- a/lib/iris/tests/results/analysis/variance_latitude.cml
+++ b/lib/iris/tests/results/analysis/variance_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="meter^-2-kilogram^2-second^-4">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="meter^-2-kilogram^2-second^-4">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/variance_latitude_longitude.cml b/lib/iris/tests/results/analysis/variance_latitude_longitude.cml
index 82ef78a4ee..45f1e63943 100644
--- a/lib/iris/tests/results/analysis/variance_latitude_longitude.cml
+++ b/lib/iris/tests/results/analysis/variance_latitude_longitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="meter^-4-kilogram^4-second^-8">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="meter^-4-kilogram^4-second^-8">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/variance_latitude_longitude_1call.cml b/lib/iris/tests/results/analysis/variance_latitude_longitude_1call.cml
index 531ec056b7..1fe09f9080 100644
--- a/lib/iris/tests/results/analysis/variance_latitude_longitude_1call.cml
+++ b/lib/iris/tests/results/analysis/variance_latitude_longitude_1call.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_pressure_at_sea_level" units="meter^-2-kilogram^2-second^-4">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_pressure_at_sea_level" units="meter^-2-kilogram^2-second^-4">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/analysis/weighted_mean_original.cml b/lib/iris/tests/results/analysis/weighted_mean_original.cml
index 2779549286..ad7063d025 100644
--- a/lib/iris/tests/results/analysis/weighted_mean_original.cml
+++ b/lib/iris/tests/results/analysis/weighted_mean_original.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="9999.0" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cdm/extract/lat_eq_10.cml b/lib/iris/tests/results/cdm/extract/lat_eq_10.cml
index 2c8d99f40c..01879b3318 100644
--- a/lib/iris/tests/results/cdm/extract/lat_eq_10.cml
+++ b/lib/iris/tests/results/cdm/extract/lat_eq_10.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cdm/extract/lat_gt_10.cml b/lib/iris/tests/results/cdm/extract/lat_gt_10.cml
index c9c96744d4..57f8c3ff84 100644
--- a/lib/iris/tests/results/cdm/extract/lat_gt_10.cml
+++ b/lib/iris/tests/results/cdm/extract/lat_gt_10.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cdm/extract/lat_gt_10_and_lon_ge_10.cml b/lib/iris/tests/results/cdm/extract/lat_gt_10_and_lon_ge_10.cml
index a5115f079b..cbf6ae670f 100644
--- a/lib/iris/tests/results/cdm/extract/lat_gt_10_and_lon_ge_10.cml
+++ b/lib/iris/tests/results/cdm/extract/lat_gt_10_and_lon_ge_10.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cdm/masked_cube.cml b/lib/iris/tests/results/cdm/masked_cube.cml
index f281e3f192..5a1577dd20 100644
--- a/lib/iris/tests/results/cdm/masked_cube.cml
+++ b/lib/iris/tests/results/cdm/masked_cube.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="1e-09" units="unknown">
+  <cube core-dtype="float32" dtype="float32" units="unknown">
     <attributes>
       <attribute name="STASH" value="m01s00i???"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/concatenate/concat_2y2d.cml b/lib/iris/tests/results/concatenate/concat_2y2d.cml
index 533cadc621..9c11ea11ba 100644
--- a/lib/iris/tests/results/concatenate/concat_2y2d.cml
+++ b/lib/iris/tests/results/concatenate/concat_2y2d.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="1234.0" units="unknown">
+  <cube core-dtype="float32" dtype="float32" units="unknown">
     <coords>
       <coord datadims="[1]">
         <dimCoord bounds="[[-0.5, 0.5],
diff --git a/lib/iris/tests/results/concatenate/concat_masked_2y2d_int16.cml b/lib/iris/tests/results/concatenate/concat_masked_2y2d_int16.cml
index 907e4e989c..dee2d36ae2 100644
--- a/lib/iris/tests/results/concatenate/concat_masked_2y2d_int16.cml
+++ b/lib/iris/tests/results/concatenate/concat_masked_2y2d_int16.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="int16" dtype="int16" fill_value="-37" units="unknown">
+  <cube core-dtype="int16" dtype="int16" units="unknown">
     <coords>
       <coord datadims="[1]">
         <dimCoord bounds="[[-0.5, 0.5],
diff --git a/lib/iris/tests/results/constrained_load/all_10_load_match.cml b/lib/iris/tests/results/constrained_load/all_10_load_match.cml
index 6ef6014182..d5808ed2f0 100644
--- a/lib/iris/tests/results/constrained_load/all_10_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/all_10_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -51,7 +51,7 @@
     </cellMethods>
     <data checksum="0x45a44f1a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="specific_humidity" units="kg kg-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="specific_humidity" units="kg kg-1">
     <attributes>
       <attribute name="STASH" value="m01s00i010"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -102,7 +102,7 @@
     </cellMethods>
     <data checksum="0x0f9c7d63" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -154,7 +154,7 @@
     </cellMethods>
     <data checksum="0xd841777e" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/all_ml_10_22_load_match.cml b/lib/iris/tests/results/constrained_load/all_ml_10_22_load_match.cml
index 73eeb4dc7f..c2803db131 100644
--- a/lib/iris/tests/results/constrained_load/all_ml_10_22_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/all_ml_10_22_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -53,7 +53,7 @@
     </cellMethods>
     <data checksum="0x152ab762" dtype="float32" shape="(2, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="specific_humidity" units="kg kg-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="specific_humidity" units="kg kg-1">
     <attributes>
       <attribute name="STASH" value="m01s00i010"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -106,7 +106,7 @@
     </cellMethods>
     <data checksum="0x38f24240" dtype="float32" shape="(2, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -160,7 +160,7 @@
     </cellMethods>
     <data checksum="0x777b79f0" dtype="float32" shape="(2, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/attribute_constraint.cml b/lib/iris/tests/results/constrained_load/attribute_constraint.cml
index 9736c2ac22..f81d8ee0d2 100644
--- a/lib/iris/tests/results/constrained_load/attribute_constraint.cml
+++ b/lib/iris/tests/results/constrained_load/attribute_constraint.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="my_attribute" value="foobar"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_10_and_theta_level_gt_30_le_3_load_match.cml b/lib/iris/tests/results/constrained_load/theta_10_and_theta_level_gt_30_le_3_load_match.cml
index 83e82d5d06..6d1c955fbd 100644
--- a/lib/iris/tests/results/constrained_load/theta_10_and_theta_level_gt_30_le_3_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/theta_10_and_theta_level_gt_30_le_3_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -51,7 +51,7 @@
     </cellMethods>
     <data checksum="0x45a44f1a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_10_and_theta_level_gt_30_le_3_load_strict.cml b/lib/iris/tests/results/constrained_load/theta_10_and_theta_level_gt_30_le_3_load_strict.cml
index 83e82d5d06..6d1c955fbd 100644
--- a/lib/iris/tests/results/constrained_load/theta_10_and_theta_level_gt_30_le_3_load_strict.cml
+++ b/lib/iris/tests/results/constrained_load/theta_10_and_theta_level_gt_30_le_3_load_strict.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -51,7 +51,7 @@
     </cellMethods>
     <data checksum="0x45a44f1a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_10_load_match.cml b/lib/iris/tests/results/constrained_load/theta_10_load_match.cml
index a7574c485d..6b6db0b26f 100644
--- a/lib/iris/tests/results/constrained_load/theta_10_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/theta_10_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_10_load_strict.cml b/lib/iris/tests/results/constrained_load/theta_10_load_strict.cml
index a7574c485d..6b6db0b26f 100644
--- a/lib/iris/tests/results/constrained_load/theta_10_load_strict.cml
+++ b/lib/iris/tests/results/constrained_load/theta_10_load_strict.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_and_all_10_load_match.cml b/lib/iris/tests/results/constrained_load/theta_and_all_10_load_match.cml
index 2d3c5be943..e919278bdb 100644
--- a/lib/iris/tests/results/constrained_load/theta_and_all_10_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/theta_and_all_10_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -140,7 +140,7 @@
     </cellMethods>
     <data checksum="0x7b0108a9" dtype="float32" shape="(38, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -191,7 +191,7 @@
     </cellMethods>
     <data checksum="0x45a44f1a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="specific_humidity" units="kg kg-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="specific_humidity" units="kg kg-1">
     <attributes>
       <attribute name="STASH" value="m01s00i010"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -242,7 +242,7 @@
     </cellMethods>
     <data checksum="0x0f9c7d63" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -294,7 +294,7 @@
     </cellMethods>
     <data checksum="0xd841777e" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_and_theta_10_load_strict.cml b/lib/iris/tests/results/constrained_load/theta_and_theta_10_load_strict.cml
index 80f4ed9f5b..081aebcd27 100644
--- a/lib/iris/tests/results/constrained_load/theta_and_theta_10_load_strict.cml
+++ b/lib/iris/tests/results/constrained_load/theta_and_theta_10_load_strict.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -140,7 +140,7 @@
     </cellMethods>
     <data checksum="0x7b0108a9" dtype="float32" shape="(38, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_and_theta_load_match.cml b/lib/iris/tests/results/constrained_load/theta_and_theta_load_match.cml
index f1c5f05f0a..04a3467b75 100644
--- a/lib/iris/tests/results/constrained_load/theta_and_theta_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/theta_and_theta_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -140,7 +140,7 @@
     </cellMethods>
     <data checksum="0x7b0108a9" dtype="float32" shape="(38, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_and_theta_load_strict.cml b/lib/iris/tests/results/constrained_load/theta_and_theta_load_strict.cml
index f1c5f05f0a..04a3467b75 100644
--- a/lib/iris/tests/results/constrained_load/theta_and_theta_load_strict.cml
+++ b/lib/iris/tests/results/constrained_load/theta_and_theta_load_strict.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -140,7 +140,7 @@
     </cellMethods>
     <data checksum="0x7b0108a9" dtype="float32" shape="(38, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_gt_30_le_3_load_match.cml b/lib/iris/tests/results/constrained_load/theta_gt_30_le_3_load_match.cml
index 03642e12d1..ea9ea1d3a3 100644
--- a/lib/iris/tests/results/constrained_load/theta_gt_30_le_3_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/theta_gt_30_le_3_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_gt_30_le_3_load_strict.cml b/lib/iris/tests/results/constrained_load/theta_gt_30_le_3_load_strict.cml
index 03642e12d1..ea9ea1d3a3 100644
--- a/lib/iris/tests/results/constrained_load/theta_gt_30_le_3_load_strict.cml
+++ b/lib/iris/tests/results/constrained_load/theta_gt_30_le_3_load_strict.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_lat_30_load_match.cml b/lib/iris/tests/results/constrained_load/theta_lat_30_load_match.cml
index cfe94f04a6..3e37596f71 100644
--- a/lib/iris/tests/results/constrained_load/theta_lat_30_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/theta_lat_30_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_lat_30_load_strict.cml b/lib/iris/tests/results/constrained_load/theta_lat_30_load_strict.cml
index cfe94f04a6..3e37596f71 100644
--- a/lib/iris/tests/results/constrained_load/theta_lat_30_load_strict.cml
+++ b/lib/iris/tests/results/constrained_load/theta_lat_30_load_strict.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_lat_gt_30_load_match.cml b/lib/iris/tests/results/constrained_load/theta_lat_gt_30_load_match.cml
index 97a518f433..42fda871e2 100644
--- a/lib/iris/tests/results/constrained_load/theta_lat_gt_30_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/theta_lat_gt_30_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_lat_gt_30_load_strict.cml b/lib/iris/tests/results/constrained_load/theta_lat_gt_30_load_strict.cml
index 97a518f433..42fda871e2 100644
--- a/lib/iris/tests/results/constrained_load/theta_lat_gt_30_load_strict.cml
+++ b/lib/iris/tests/results/constrained_load/theta_lat_gt_30_load_strict.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_load_match.cml b/lib/iris/tests/results/constrained_load/theta_load_match.cml
index f80d9e072a..f976e656f9 100644
--- a/lib/iris/tests/results/constrained_load/theta_load_match.cml
+++ b/lib/iris/tests/results/constrained_load/theta_load_match.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/constrained_load/theta_load_strict.cml b/lib/iris/tests/results/constrained_load/theta_load_strict.cml
index f80d9e072a..f976e656f9 100644
--- a/lib/iris/tests/results/constrained_load/theta_load_strict.cml
+++ b/lib/iris/tests/results/constrained_load/theta_load_strict.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cube_io/pickling/cubelist.cml b/lib/iris/tests/results/cube_io/pickling/cubelist.cml
index c2b7f60194..f53bacfb6f 100644
--- a/lib/iris/tests/results/cube_io/pickling/cubelist.cml
+++ b/lib/iris/tests/results/cube_io/pickling/cubelist.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -516,7 +516,7 @@
     <cellMethods/>
     <data checksum="0x7a31dc88" dtype="float32" shape="(6, 70, 100, 100)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="surface_altitude" units="m">
+  <cube core-dtype="float32" dtype="float32" standard_name="surface_altitude" units="m">
     <attributes>
       <attribute name="STASH" value="m01s00i033"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cube_io/pickling/single_cube.cml b/lib/iris/tests/results/cube_io/pickling/single_cube.cml
index d793a391f6..3df9dd7602 100644
--- a/lib/iris/tests/results/cube_io/pickling/single_cube.cml
+++ b/lib/iris/tests/results/cube_io/pickling/single_cube.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cube_io/pickling/theta.cml b/lib/iris/tests/results/cube_io/pickling/theta.cml
index c3d1825cd2..a85fccd62e 100644
--- a/lib/iris/tests/results/cube_io/pickling/theta.cml
+++ b/lib/iris/tests/results/cube_io/pickling/theta.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cube_io/pp/load/global.cml b/lib/iris/tests/results/cube_io/pp/load/global.cml
index 2779549286..ad7063d025 100644
--- a/lib/iris/tests/results/cube_io/pp/load/global.cml
+++ b/lib/iris/tests/results/cube_io/pp/load/global.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="9999.0" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing1.cml b/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing1.cml
index 8693d1222d..30beb4ef20 100644
--- a/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing1.cml
+++ b/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing1.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing2.cml b/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing2.cml
index 1e01200db9..2655740cf8 100644
--- a/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing2.cml
+++ b/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing2.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing3.cml b/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing3.cml
index 439d183b19..e113bf4ac9 100644
--- a/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing3.cml
+++ b/lib/iris/tests/results/cube_slice/real_data_dual_tuple_indexing3.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/cube_slice/real_empty_data_indexing.cml b/lib/iris/tests/results/cube_slice/real_empty_data_indexing.cml
index e61668baa3..74be87f6a5 100644
--- a/lib/iris/tests/results/cube_slice/real_empty_data_indexing.cml
+++ b/lib/iris/tests/results/cube_slice/real_empty_data_indexing.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure_at_sea_level" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s16i222"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadFF/simple.cml b/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadFF/simple.cml
index 5cb0de933c..9d985a7ae8 100644
--- a/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadFF/simple.cml
+++ b/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadFF/simple.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s00i407"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadFF/simple_callback.cml b/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadFF/simple_callback.cml
index 62126aa03b..daf98f9dbd 100644
--- a/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadFF/simple_callback.cml
+++ b/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadFF/simple_callback.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s00i407"/>
       <attribute name="processing" value="fast-ff"/>
diff --git a/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadPP/simple.cml b/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadPP/simple.cml
index cc062c176a..1ff0282592 100644
--- a/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadPP/simple.cml
+++ b/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadPP/simple.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s00i407"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadPP/simple_callback.cml b/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadPP/simple_callback.cml
index 9c955e24d7..4f2ad1aca3 100644
--- a/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadPP/simple_callback.cml
+++ b/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadPP/simple_callback.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s00i407"/>
       <attribute name="processing" value="fast-pp"/>
diff --git a/lib/iris/tests/results/file_load/theta_levels.cml b/lib/iris/tests/results/file_load/theta_levels.cml
index abd5f6ce84..ac4d7f04c1 100644
--- a/lib/iris/tests/results/file_load/theta_levels.cml
+++ b/lib/iris/tests/results/file_load/theta_levels.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -51,7 +51,7 @@
     </cellMethods>
     <data checksum="0x17763b08" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -102,7 +102,7 @@
     </cellMethods>
     <data checksum="0xc185be42" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -153,7 +153,7 @@
     </cellMethods>
     <data checksum="0xe65750bc" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -204,7 +204,7 @@
     </cellMethods>
     <data checksum="0x816283f9" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -255,7 +255,7 @@
     </cellMethods>
     <data checksum="0x56b85efa" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -306,7 +306,7 @@
     </cellMethods>
     <data checksum="0xe96a203f" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -357,7 +357,7 @@
     </cellMethods>
     <data checksum="0xce07f637" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -408,7 +408,7 @@
     </cellMethods>
     <data checksum="0x1cfc905c" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -459,7 +459,7 @@
     </cellMethods>
     <data checksum="0xe239fdec" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -510,7 +510,7 @@
     </cellMethods>
     <data checksum="0x45a44f1a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -561,7 +561,7 @@
     </cellMethods>
     <data checksum="0xb12f6572" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -612,7 +612,7 @@
     </cellMethods>
     <data checksum="0x0e3c5965" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -663,7 +663,7 @@
     </cellMethods>
     <data checksum="0x6347d5bd" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -714,7 +714,7 @@
     </cellMethods>
     <data checksum="0x77273f7e" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -765,7 +765,7 @@
     </cellMethods>
     <data checksum="0x4bd3a5eb" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -816,7 +816,7 @@
     </cellMethods>
     <data checksum="0x129ae43d" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -867,7 +867,7 @@
     </cellMethods>
     <data checksum="0x10f0c12e" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -918,7 +918,7 @@
     </cellMethods>
     <data checksum="0x2bb76c16" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -969,7 +969,7 @@
     </cellMethods>
     <data checksum="0xf5b26d1a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1020,7 +1020,7 @@
     </cellMethods>
     <data checksum="0x9b8c7031" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1071,7 +1071,7 @@
     </cellMethods>
     <data checksum="0xc310cc9a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1122,7 +1122,7 @@
     </cellMethods>
     <data checksum="0xb41fa10f" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1173,7 +1173,7 @@
     </cellMethods>
     <data checksum="0xefab27e4" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1224,7 +1224,7 @@
     </cellMethods>
     <data checksum="0x946cabe8" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1275,7 +1275,7 @@
     </cellMethods>
     <data checksum="0x5998cbc6" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1326,7 +1326,7 @@
     </cellMethods>
     <data checksum="0xb0a6552e" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1377,7 +1377,7 @@
     </cellMethods>
     <data checksum="0xab0a810b" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1428,7 +1428,7 @@
     </cellMethods>
     <data checksum="0x9ab0fdd8" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1479,7 +1479,7 @@
     </cellMethods>
     <data checksum="0x34f06e6a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1530,7 +1530,7 @@
     </cellMethods>
     <data checksum="0x47c31d91" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1581,7 +1581,7 @@
     </cellMethods>
     <data checksum="0x8569fd3f" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1632,7 +1632,7 @@
     </cellMethods>
     <data checksum="0x3ace76f3" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1683,7 +1683,7 @@
     </cellMethods>
     <data checksum="0xbc11c8a9" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1734,7 +1734,7 @@
     </cellMethods>
     <data checksum="0xbf693c7d" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1785,7 +1785,7 @@
     </cellMethods>
     <data checksum="0xc100ff09" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1836,7 +1836,7 @@
     </cellMethods>
     <data checksum="0x43595449" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1887,7 +1887,7 @@
     </cellMethods>
     <data checksum="0x377b59d4" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/file_load/u_wind_levels.cml b/lib/iris/tests/results/file_load/u_wind_levels.cml
index c0b5a76a34..763b56186d 100644
--- a/lib/iris/tests/results/file_load/u_wind_levels.cml
+++ b/lib/iris/tests/results/file_load/u_wind_levels.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -52,7 +52,7 @@
     </cellMethods>
     <data checksum="0x127b39e8" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -104,7 +104,7 @@
     </cellMethods>
     <data checksum="0x088c4545" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -156,7 +156,7 @@
     </cellMethods>
     <data checksum="0xc896dcd3" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -208,7 +208,7 @@
     </cellMethods>
     <data checksum="0x3df23f98" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -260,7 +260,7 @@
     </cellMethods>
     <data checksum="0xa97d11dd" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -312,7 +312,7 @@
     </cellMethods>
     <data checksum="0x24173b24" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -364,7 +364,7 @@
     </cellMethods>
     <data checksum="0x16761c14" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -416,7 +416,7 @@
     </cellMethods>
     <data checksum="0xf6f56e25" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -468,7 +468,7 @@
     </cellMethods>
     <data checksum="0x57a3823b" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -520,7 +520,7 @@
     </cellMethods>
     <data checksum="0xd841777e" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -572,7 +572,7 @@
     </cellMethods>
     <data checksum="0xc43c2a0b" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -624,7 +624,7 @@
     </cellMethods>
     <data checksum="0x08bf7abd" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -676,7 +676,7 @@
     </cellMethods>
     <data checksum="0x5870c1e0" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -728,7 +728,7 @@
     </cellMethods>
     <data checksum="0x7cac5103" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -780,7 +780,7 @@
     </cellMethods>
     <data checksum="0xcd2d62b1" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -832,7 +832,7 @@
     </cellMethods>
     <data checksum="0x4e1b7ef5" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -884,7 +884,7 @@
     </cellMethods>
     <data checksum="0x104081c2" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -936,7 +936,7 @@
     </cellMethods>
     <data checksum="0x392ef79f" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -988,7 +988,7 @@
     </cellMethods>
     <data checksum="0xdf6dbef7" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1040,7 +1040,7 @@
     </cellMethods>
     <data checksum="0x871b4ee8" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1092,7 +1092,7 @@
     </cellMethods>
     <data checksum="0x3cee95b4" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1144,7 +1144,7 @@
     </cellMethods>
     <data checksum="0x76208cc7" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1196,7 +1196,7 @@
     </cellMethods>
     <data checksum="0xa0f56a0a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1248,7 +1248,7 @@
     </cellMethods>
     <data checksum="0xc5654966" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1300,7 +1300,7 @@
     </cellMethods>
     <data checksum="0xde1441e7" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1352,7 +1352,7 @@
     </cellMethods>
     <data checksum="0xf70c5634" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1404,7 +1404,7 @@
     </cellMethods>
     <data checksum="0xe2d29281" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1456,7 +1456,7 @@
     </cellMethods>
     <data checksum="0xcfe34b4d" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1508,7 +1508,7 @@
     </cellMethods>
     <data checksum="0x4cb07673" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1560,7 +1560,7 @@
     </cellMethods>
     <data checksum="0x47c8d38a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1612,7 +1612,7 @@
     </cellMethods>
     <data checksum="0x6c15a2c3" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1664,7 +1664,7 @@
     </cellMethods>
     <data checksum="0xb922530c" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1716,7 +1716,7 @@
     </cellMethods>
     <data checksum="0x5020a5d1" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1768,7 +1768,7 @@
     </cellMethods>
     <data checksum="0xe308ebfa" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1820,7 +1820,7 @@
     </cellMethods>
     <data checksum="0x50f626b0" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1872,7 +1872,7 @@
     </cellMethods>
     <data checksum="0x19624929" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1924,7 +1924,7 @@
     </cellMethods>
     <data checksum="0x4c54b2ff" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/file_load/v_wind_levels.cml b/lib/iris/tests/results/file_load/v_wind_levels.cml
index f8fe971f90..e4e3709a13 100644
--- a/lib/iris/tests/results/file_load/v_wind_levels.cml
+++ b/lib/iris/tests/results/file_load/v_wind_levels.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -52,7 +52,7 @@
     </cellMethods>
     <data checksum="0x50e427ed" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -104,7 +104,7 @@
     </cellMethods>
     <data checksum="0xa4593dbf" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -156,7 +156,7 @@
     </cellMethods>
     <data checksum="0x00ff91f2" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -208,7 +208,7 @@
     </cellMethods>
     <data checksum="0xa03492c0" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -260,7 +260,7 @@
     </cellMethods>
     <data checksum="0xc61368b3" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -312,7 +312,7 @@
     </cellMethods>
     <data checksum="0x9a20e5c6" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -364,7 +364,7 @@
     </cellMethods>
     <data checksum="0xfbcb2a96" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -416,7 +416,7 @@
     </cellMethods>
     <data checksum="0x31c19cd4" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -468,7 +468,7 @@
     </cellMethods>
     <data checksum="0x6b0cc25a" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -520,7 +520,7 @@
     </cellMethods>
     <data checksum="0x31d04486" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -572,7 +572,7 @@
     </cellMethods>
     <data checksum="0x7e2cc5b6" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -624,7 +624,7 @@
     </cellMethods>
     <data checksum="0x26741d4b" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -676,7 +676,7 @@
     </cellMethods>
     <data checksum="0x2c2d97dd" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -728,7 +728,7 @@
     </cellMethods>
     <data checksum="0x6a294180" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -780,7 +780,7 @@
     </cellMethods>
     <data checksum="0x92eb6ab4" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -832,7 +832,7 @@
     </cellMethods>
     <data checksum="0x39456c40" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -884,7 +884,7 @@
     </cellMethods>
     <data checksum="0x4963cfd6" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -936,7 +936,7 @@
     </cellMethods>
     <data checksum="0xe81e8be7" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -988,7 +988,7 @@
     </cellMethods>
     <data checksum="0xfb9b0ed6" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1040,7 +1040,7 @@
     </cellMethods>
     <data checksum="0x2057f49e" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1092,7 +1092,7 @@
     </cellMethods>
     <data checksum="0x9bb6020a" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1144,7 +1144,7 @@
     </cellMethods>
     <data checksum="0x05970b5d" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1196,7 +1196,7 @@
     </cellMethods>
     <data checksum="0xb013389c" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1248,7 +1248,7 @@
     </cellMethods>
     <data checksum="0x208fa829" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1300,7 +1300,7 @@
     </cellMethods>
     <data checksum="0xe2582bbd" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1352,7 +1352,7 @@
     </cellMethods>
     <data checksum="0xb964b7d7" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1404,7 +1404,7 @@
     </cellMethods>
     <data checksum="0xc8a5b95e" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1456,7 +1456,7 @@
     </cellMethods>
     <data checksum="0x4bd4eae9" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1508,7 +1508,7 @@
     </cellMethods>
     <data checksum="0xe0549b09" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1560,7 +1560,7 @@
     </cellMethods>
     <data checksum="0xf6e3546d" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1612,7 +1612,7 @@
     </cellMethods>
     <data checksum="0x5525ab2a" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1664,7 +1664,7 @@
     </cellMethods>
     <data checksum="0xb48c5eb1" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1716,7 +1716,7 @@
     </cellMethods>
     <data checksum="0xcfb28f0d" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1768,7 +1768,7 @@
     </cellMethods>
     <data checksum="0x4290df26" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1820,7 +1820,7 @@
     </cellMethods>
     <data checksum="0x82c0d953" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1872,7 +1872,7 @@
     </cellMethods>
     <data checksum="0x49202448" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1924,7 +1924,7 @@
     </cellMethods>
     <data checksum="0x04b1c44c" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/file_load/wind_levels.cml b/lib/iris/tests/results/file_load/wind_levels.cml
index 8fba633749..3c4bf37ae8 100644
--- a/lib/iris/tests/results/file_load/wind_levels.cml
+++ b/lib/iris/tests/results/file_load/wind_levels.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -52,7 +52,7 @@
     </cellMethods>
     <data checksum="0x127b39e8" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -104,7 +104,7 @@
     </cellMethods>
     <data checksum="0x088c4545" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -156,7 +156,7 @@
     </cellMethods>
     <data checksum="0xc896dcd3" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -208,7 +208,7 @@
     </cellMethods>
     <data checksum="0x3df23f98" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -260,7 +260,7 @@
     </cellMethods>
     <data checksum="0xa97d11dd" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -312,7 +312,7 @@
     </cellMethods>
     <data checksum="0x24173b24" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -364,7 +364,7 @@
     </cellMethods>
     <data checksum="0x16761c14" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -416,7 +416,7 @@
     </cellMethods>
     <data checksum="0xf6f56e25" dtype="float32" shape="(145, 192)"/>
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-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -468,7 +468,7 @@
     </cellMethods>
     <data checksum="0x57a3823b" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -520,7 +520,7 @@
     </cellMethods>
     <data checksum="0xd841777e" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -572,7 +572,7 @@
     </cellMethods>
     <data checksum="0xc43c2a0b" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -624,7 +624,7 @@
     </cellMethods>
     <data checksum="0x08bf7abd" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -676,7 +676,7 @@
     </cellMethods>
     <data checksum="0x5870c1e0" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -728,7 +728,7 @@
     </cellMethods>
     <data checksum="0x7cac5103" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -780,7 +780,7 @@
     </cellMethods>
     <data checksum="0xcd2d62b1" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -832,7 +832,7 @@
     </cellMethods>
     <data checksum="0x4e1b7ef5" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -884,7 +884,7 @@
     </cellMethods>
     <data checksum="0x104081c2" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -936,7 +936,7 @@
     </cellMethods>
     <data checksum="0x392ef79f" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -988,7 +988,7 @@
     </cellMethods>
     <data checksum="0xdf6dbef7" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1040,7 +1040,7 @@
     </cellMethods>
     <data checksum="0x871b4ee8" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1092,7 +1092,7 @@
     </cellMethods>
     <data checksum="0x3cee95b4" dtype="float32" shape="(145, 192)"/>
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-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1144,7 +1144,7 @@
     </cellMethods>
     <data checksum="0x76208cc7" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1196,7 +1196,7 @@
     </cellMethods>
     <data checksum="0xa0f56a0a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1248,7 +1248,7 @@
     </cellMethods>
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   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1300,7 +1300,7 @@
     </cellMethods>
     <data checksum="0xde1441e7" dtype="float32" shape="(145, 192)"/>
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-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1352,7 +1352,7 @@
     </cellMethods>
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   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1404,7 +1404,7 @@
     </cellMethods>
     <data checksum="0xe2d29281" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1456,7 +1456,7 @@
     </cellMethods>
     <data checksum="0xcfe34b4d" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1508,7 +1508,7 @@
     </cellMethods>
     <data checksum="0x4cb07673" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1560,7 +1560,7 @@
     </cellMethods>
     <data checksum="0x47c8d38a" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1612,7 +1612,7 @@
     </cellMethods>
     <data checksum="0x6c15a2c3" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1664,7 +1664,7 @@
     </cellMethods>
     <data checksum="0xb922530c" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1716,7 +1716,7 @@
     </cellMethods>
     <data checksum="0x5020a5d1" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1768,7 +1768,7 @@
     </cellMethods>
     <data checksum="0xe308ebfa" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1820,7 +1820,7 @@
     </cellMethods>
     <data checksum="0x50f626b0" dtype="float32" shape="(145, 192)"/>
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-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1872,7 +1872,7 @@
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   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1924,7 +1924,7 @@
     </cellMethods>
     <data checksum="0x4c54b2ff" dtype="float32" shape="(145, 192)"/>
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-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -1976,7 +1976,7 @@
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     <data checksum="0x4cd24d81" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2028,7 +2028,7 @@
     </cellMethods>
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   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2080,7 +2080,7 @@
     </cellMethods>
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   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2132,7 +2132,7 @@
     </cellMethods>
     <data checksum="0x00ff91f2" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2184,7 +2184,7 @@
     </cellMethods>
     <data checksum="0xa03492c0" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2236,7 +2236,7 @@
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   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2288,7 +2288,7 @@
     </cellMethods>
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-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2340,7 +2340,7 @@
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     <data checksum="0xfbcb2a96" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2392,7 +2392,7 @@
     </cellMethods>
     <data checksum="0x31c19cd4" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2444,7 +2444,7 @@
     </cellMethods>
     <data checksum="0x6b0cc25a" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2496,7 +2496,7 @@
     </cellMethods>
     <data checksum="0x31d04486" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2548,7 +2548,7 @@
     </cellMethods>
     <data checksum="0x7e2cc5b6" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2600,7 +2600,7 @@
     </cellMethods>
     <data checksum="0x26741d4b" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2652,7 +2652,7 @@
     </cellMethods>
     <data checksum="0x2c2d97dd" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2704,7 +2704,7 @@
     </cellMethods>
     <data checksum="0x6a294180" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2756,7 +2756,7 @@
     </cellMethods>
     <data checksum="0x92eb6ab4" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2808,7 +2808,7 @@
     </cellMethods>
     <data checksum="0x39456c40" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2860,7 +2860,7 @@
     </cellMethods>
     <data checksum="0x4963cfd6" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2912,7 +2912,7 @@
     </cellMethods>
     <data checksum="0xe81e8be7" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -2964,7 +2964,7 @@
     </cellMethods>
     <data checksum="0xfb9b0ed6" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3016,7 +3016,7 @@
     </cellMethods>
     <data checksum="0x2057f49e" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3068,7 +3068,7 @@
     </cellMethods>
     <data checksum="0x9bb6020a" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3120,7 +3120,7 @@
     </cellMethods>
     <data checksum="0x05970b5d" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3172,7 +3172,7 @@
     </cellMethods>
     <data checksum="0xb013389c" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3224,7 +3224,7 @@
     </cellMethods>
     <data checksum="0x208fa829" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3276,7 +3276,7 @@
     </cellMethods>
     <data checksum="0xe2582bbd" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3328,7 +3328,7 @@
     </cellMethods>
     <data checksum="0xb964b7d7" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3380,7 +3380,7 @@
     </cellMethods>
     <data checksum="0xc8a5b95e" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3432,7 +3432,7 @@
     </cellMethods>
     <data checksum="0x4bd4eae9" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3484,7 +3484,7 @@
     </cellMethods>
     <data checksum="0xe0549b09" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3536,7 +3536,7 @@
     </cellMethods>
     <data checksum="0xf6e3546d" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3588,7 +3588,7 @@
     </cellMethods>
     <data checksum="0x5525ab2a" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3640,7 +3640,7 @@
     </cellMethods>
     <data checksum="0xb48c5eb1" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3692,7 +3692,7 @@
     </cellMethods>
     <data checksum="0xcfb28f0d" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3744,7 +3744,7 @@
     </cellMethods>
     <data checksum="0x4290df26" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3796,7 +3796,7 @@
     </cellMethods>
     <data checksum="0x82c0d953" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3848,7 +3848,7 @@
     </cellMethods>
     <data checksum="0x49202448" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -3900,7 +3900,7 @@
     </cellMethods>
     <data checksum="0x04b1c44c" dtype="float32" shape="(144, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/merge/dec.cml b/lib/iris/tests/results/merge/dec.cml
index 57e4a0eae0..f26ee2048c 100644
--- a/lib/iris/tests/results/merge/dec.cml
+++ b/lib/iris/tests/results/merge/dec.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -140,7 +140,7 @@
     </cellMethods>
     <data checksum="0x7b0108a9" dtype="float32" shape="(38, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="specific_humidity" units="kg kg-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="specific_humidity" units="kg kg-1">
     <attributes>
       <attribute name="STASH" value="m01s00i010"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -280,7 +280,7 @@
     </cellMethods>
     <data checksum="0x28056617" dtype="float32" shape="(38, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="x_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="x_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i002"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -421,7 +421,7 @@
     </cellMethods>
     <data checksum="0xe099eee0" dtype="float32" shape="(38, 145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="y_wind" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="y_wind" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s00i003"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/merge/theta.cml b/lib/iris/tests/results/merge/theta.cml
index f80d9e072a..f976e656f9 100644
--- a/lib/iris/tests/results/merge/theta.cml
+++ b/lib/iris/tests/results/merge/theta.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/merge/theta_two_times.cml b/lib/iris/tests/results/merge/theta_two_times.cml
index bed9f06208..6b99b63d8b 100644
--- a/lib/iris/tests/results/merge/theta_two_times.cml
+++ b/lib/iris/tests/results/merge/theta_two_times.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_cell_methods.cml b/lib/iris/tests/results/netcdf/netcdf_cell_methods.cml
index c50b6915e6..5a5b010d7b 100644
--- a/lib/iris/tests/results/netcdf/netcdf_cell_methods.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_cell_methods.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_axes_0" units="1" var_name="cube_axes_0">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_axes_0" units="1" var_name="cube_axes_0">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -20,7 +20,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_axes_1" units="1" var_name="cube_axes_1">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_axes_1" units="1" var_name="cube_axes_1">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -41,7 +41,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_axes_2" units="1" var_name="cube_axes_2">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_axes_2" units="1" var_name="cube_axes_2">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -66,7 +66,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_axes_3" units="1" var_name="cube_axes_3">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_axes_3" units="1" var_name="cube_axes_3">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -89,7 +89,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_axes_4" units="1" var_name="cube_axes_4">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_axes_4" units="1" var_name="cube_axes_4">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -112,7 +112,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_comment_0" units="1" var_name="cube_comment_0">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_comment_0" units="1" var_name="cube_comment_0">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -131,7 +131,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_comment_1" units="1" var_name="cube_comment_1">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_comment_1" units="1" var_name="cube_comment_1">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -150,7 +150,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_comment_2" units="1" var_name="cube_comment_2">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_comment_2" units="1" var_name="cube_comment_2">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -170,7 +170,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_comment_3" units="1" var_name="cube_comment_3">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_comment_3" units="1" var_name="cube_comment_3">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -190,7 +190,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_comment_4" units="1" var_name="cube_comment_4">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_comment_4" units="1" var_name="cube_comment_4">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -213,7 +213,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_interval_0" units="1" var_name="cube_interval_0">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_interval_0" units="1" var_name="cube_interval_0">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -232,7 +232,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_interval_1" units="1" var_name="cube_interval_1">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_interval_1" units="1" var_name="cube_interval_1">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -252,7 +252,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_interval_2" units="1" var_name="cube_interval_2">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_interval_2" units="1" var_name="cube_interval_2">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -272,7 +272,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_interval_3" units="1" var_name="cube_interval_3">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_interval_3" units="1" var_name="cube_interval_3">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -295,7 +295,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_interval_4" units="1" var_name="cube_interval_4">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_interval_4" units="1" var_name="cube_interval_4">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -320,7 +320,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_maximum" units="1" var_name="cube_maximum">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_maximum" units="1" var_name="cube_maximum">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
@@ -333,7 +333,7 @@
     </cellMethods>
     <data checksum="0x2144df1c" dtype="int32" mask_checksum="0xa505df1b" shape="(1,)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_mean" units="1" var_name="cube_mean">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_mean" units="1" var_name="cube_mean">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
@@ -346,7 +346,7 @@
     </cellMethods>
     <data checksum="0x2144df1c" dtype="int32" mask_checksum="0xa505df1b" shape="(1,)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_median" units="1" var_name="cube_median">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_median" units="1" var_name="cube_median">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
@@ -359,7 +359,7 @@
     </cellMethods>
     <data checksum="0x2144df1c" dtype="int32" mask_checksum="0xa505df1b" shape="(1,)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_mid_range" units="1" var_name="cube_mid_range">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_mid_range" units="1" var_name="cube_mid_range">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
@@ -372,7 +372,7 @@
     </cellMethods>
     <data checksum="0x2144df1c" dtype="int32" mask_checksum="0xa505df1b" shape="(1,)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_minimum" units="1" var_name="cube_minimum">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_minimum" units="1" var_name="cube_minimum">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
@@ -385,7 +385,7 @@
     </cellMethods>
     <data checksum="0x2144df1c" dtype="int32" mask_checksum="0xa505df1b" shape="(1,)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_mix_0" units="1" var_name="cube_mix_0">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_mix_0" units="1" var_name="cube_mix_0">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -404,7 +404,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_mix_1" units="1" var_name="cube_mix_1">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_mix_1" units="1" var_name="cube_mix_1">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -424,7 +424,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_mix_2" units="1" var_name="cube_mix_2">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_mix_2" units="1" var_name="cube_mix_2">
     <coords>
       <coord datadims="[1]">
         <dimCoord id="4a0cb9d8" points="[0, 1]" shape="(2,)" standard_name="latitude" units="Unit('degrees')" value_type="int32" var_name="lat"/>
@@ -447,7 +447,7 @@
     </cellMethods>
     <data checksum="0xecbb4b55" dtype="int32" mask_checksum="0xf626d399" shape="(1, 2, 2)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_mode" units="1" var_name="cube_mode">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_mode" units="1" var_name="cube_mode">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
@@ -460,7 +460,7 @@
     </cellMethods>
     <data checksum="0x2144df1c" dtype="int32" mask_checksum="0xa505df1b" shape="(1,)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_point" units="1" var_name="cube_point">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_point" units="1" var_name="cube_point">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
@@ -473,7 +473,7 @@
     </cellMethods>
     <data checksum="0x2144df1c" dtype="int32" mask_checksum="0xa505df1b" shape="(1,)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_standard_deviation" units="1" var_name="cube_standard_deviation">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_standard_deviation" units="1" var_name="cube_standard_deviation">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
@@ -486,7 +486,7 @@
     </cellMethods>
     <data checksum="0x2144df1c" dtype="int32" mask_checksum="0xa505df1b" shape="(1,)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_sum" units="1" var_name="cube_sum">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_sum" units="1" var_name="cube_sum">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
@@ -499,7 +499,7 @@
     </cellMethods>
     <data checksum="0x2144df1c" dtype="int32" mask_checksum="0xa505df1b" shape="(1,)"/>
   </cube>
-  <cube core-dtype="int32" dtype="int32" fill_value="-2147483647" long_name="cube_variance" units="1" var_name="cube_variance">
+  <cube core-dtype="int32" dtype="int32" long_name="cube_variance" units="1" var_name="cube_variance">
     <coords>
       <coord datadims="[0]">
         <dimCoord id="3a4420ff" points="[0]" shape="(1,)" standard_name="time" units="Unit('hours since 1970-1-1 00:00:00', calendar='gregorian')" value_type="int32" var_name="time"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_index_0.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_index_0.cml
index 9e03a24a45..b168b70cc9 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_index_0.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_index_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_index_1.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_index_1.cml
index eb1e569293..b04eb82915 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_index_1.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_index_1.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_index_2.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_index_2.cml
index d8d9488a0e..f8fe68740e 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_index_2.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_index_2.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_mix_0.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_mix_0.cml
index 4acbce1110..22d9a2852c 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_mix_0.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_mix_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_mix_1.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_mix_1.cml
index 72ac649c0a..4de572cdd3 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_mix_1.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_mix_1.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_slice_0.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_slice_0.cml
index 486ca6377a..7b969be669 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_slice_0.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_slice_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_slice_1.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_slice_1.cml
index d01cc81467..20b110a205 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_slice_1.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_slice_1.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_slice_2.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_slice_2.cml
index 0da72836a6..aeb13fa316 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_slice_2.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_slice_2.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_0.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_0.cml
index 760313769a..28d7299d90 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_0.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_1.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_1.cml
index f1779f48eb..bdcd53fd1e 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_1.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_1.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_2.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_2.cml
index d035b1bb6e..4a6785ea7b 100644
--- a/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_2.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_deferred_tuple_2.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_global_xyt_hires.cml b/lib/iris/tests/results/netcdf/netcdf_global_xyt_hires.cml
index 6fd892b43d..ff799e635f 100644
--- a/lib/iris/tests/results/netcdf/netcdf_global_xyt_hires.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_global_xyt_hires.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="1e+20" long_name="Zonal Surface Wind Speed" standard_name="eastward_wind" units="m s-1" var_name="uas">
+  <cube core-dtype="float32" dtype="float32" long_name="Zonal Surface Wind Speed" standard_name="eastward_wind" units="m s-1" var_name="uas">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="cmor_version" value="0.96"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_global_xyt_total.cml b/lib/iris/tests/results/netcdf/netcdf_global_xyt_total.cml
index 0d685802ca..a88e7bb3b9 100644
--- a/lib/iris/tests/results/netcdf/netcdf_global_xyt_total.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_global_xyt_total.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="Thu Feb 11 10:56:57 2010: ncks total_column_co2.nc -o SMALL_total_column_co2.nc -d time,,30
diff --git a/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems.cml b/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems.cml
index b94a1e78a3..7860db7736 100644
--- a/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Carbon Dioxide" units="kg kg**-1" var_name="co2">
+  <cube core-dtype="float64" dtype="float64" long_name="Carbon Dioxide" units="kg kg**-1" var_name="co2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="2009-08-25 13:46:31 GMT by mars2netcdf-0.92"/>
@@ -26,7 +26,7 @@
     <cellMethods/>
     <data checksum="0x65252ed2" dtype="float64" shape="(1, 60, 181, 360)"/>
   </cube>
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Logarithm of surface pressure" units="no_unit" var_name="lnsp">
+  <cube core-dtype="float64" dtype="float64" long_name="Logarithm of surface pressure" units="no_unit" var_name="lnsp">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="2009-08-25 13:46:31 GMT by mars2netcdf-0.92"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems_iter_0.cml b/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems_iter_0.cml
index 8a61b31886..1bacbc75a9 100644
--- a/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems_iter_0.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems_iter_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Carbon Dioxide" units="kg kg**-1" var_name="co2">
+  <cube core-dtype="float64" dtype="float64" long_name="Carbon Dioxide" units="kg kg**-1" var_name="co2">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="2009-08-25 13:46:31 GMT by mars2netcdf-0.92"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems_iter_1.cml b/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems_iter_1.cml
index cb0ce6d5fd..35d3220cb9 100644
--- a/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems_iter_1.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_global_xyzt_gems_iter_1.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" long_name="Logarithm of surface pressure" units="no_unit" var_name="lnsp">
+  <cube core-dtype="float64" dtype="float64" long_name="Logarithm of surface pressure" units="no_unit" var_name="lnsp">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="history" value="2009-08-25 13:46:31 GMT by mars2netcdf-0.92"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_lcc.cml b/lib/iris/tests/results/netcdf/netcdf_lcc.cml
index 9bdf866815..3916f15cc1 100644
--- a/lib/iris/tests/results/netcdf/netcdf_lcc.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_lcc.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="1e+20" long_name="Daily Mean Near-Surface Air Temperature" standard_name="air_temperature" units="Celsius" var_name="tas">
+  <cube core-dtype="float64" dtype="float64" long_name="Daily Mean Near-Surface Air Temperature" standard_name="air_temperature" units="Celsius" var_name="tas">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
       <attribute name="Note" value="This dataset is for test purposes only"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_rotated_xy_land.cml b/lib/iris/tests/results/netcdf/netcdf_rotated_xy_land.cml
index bde933568b..a9fdb2ffca 100644
--- a/lib/iris/tests/results/netcdf/netcdf_rotated_xy_land.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_rotated_xy_land.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="1e+30" long_name="land area fraction of grid cell" standard_name="land_area_fraction" units="1" var_name="sftls">
+  <cube core-dtype="float32" dtype="float32" long_name="land area fraction of grid cell" standard_name="land_area_fraction" units="1" var_name="sftls">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="conventionsURL" value="http://www.cgd.ucar.edu/cms/eaton/cf-metadata/index.html"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_rotated_xyt_precipitation.cml b/lib/iris/tests/results/netcdf/netcdf_rotated_xyt_precipitation.cml
index 3347b542c8..a5584ceb8d 100644
--- a/lib/iris/tests/results/netcdf/netcdf_rotated_xyt_precipitation.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_rotated_xyt_precipitation.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="1e+30" long_name="Precipitation" standard_name="precipitation_flux" units="kg m-2 s-1" var_name="pr">
+  <cube core-dtype="float32" dtype="float32" long_name="Precipitation" standard_name="precipitation_flux" units="kg m-2 s-1" var_name="pr">
     <attributes>
       <attribute name="Conventions" value="CF-1.0"/>
       <attribute name="NCO" value="4.1.0"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_save_load_hybrid_height.cml b/lib/iris/tests/results/netcdf/netcdf_save_load_hybrid_height.cml
index 2230369b19..8f207b126b 100644
--- a/lib/iris/tests/results/netcdf/netcdf_save_load_hybrid_height.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_save_load_hybrid_height.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K" var_name="air_potential_temperature">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K" var_name="air_potential_temperature">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
       <attribute name="STASH" value="m01s00i004"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_save_load_ndim_auxiliary.cml b/lib/iris/tests/results/netcdf/netcdf_save_load_ndim_auxiliary.cml
index 1347f87884..4f92fd1466 100644
--- a/lib/iris/tests/results/netcdf/netcdf_save_load_ndim_auxiliary.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_save_load_ndim_auxiliary.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="1e+30" long_name="Precipitation" standard_name="precipitation_flux" units="kg m-2 s-1" var_name="pr">
+  <cube core-dtype="float32" dtype="float32" long_name="Precipitation" standard_name="precipitation_flux" units="kg m-2 s-1" var_name="pr">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
       <attribute name="NCO" value="4.1.0"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_stereo.cml b/lib/iris/tests/results/netcdf/netcdf_stereo.cml
index 3a79250bf2..19750b255f 100644
--- a/lib/iris/tests/results/netcdf/netcdf_stereo.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_stereo.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" long_name="toa_brightness_temperature" standard_name="toa_brightness_temperature" units="K" var_name="data">
+  <cube core-dtype="float32" dtype="float32" long_name="toa_brightness_temperature" standard_name="toa_brightness_temperature" units="K" var_name="data">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
       <attribute name="Note" value="This dataset is for test purposes only"/>
diff --git a/lib/iris/tests/results/netcdf/netcdf_tmerc_and_climatology.cml b/lib/iris/tests/results/netcdf/netcdf_tmerc_and_climatology.cml
index ccfdbf6a90..2850984e75 100644
--- a/lib/iris/tests/results/netcdf/netcdf_tmerc_and_climatology.cml
+++ b/lib/iris/tests/results/netcdf/netcdf_tmerc_and_climatology.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-9999.0" long_name="Mean temperature" units="degrees_celsius" var_name="tmean">
+  <cube core-dtype="float32" dtype="float32" long_name="Mean temperature" units="degrees_celsius" var_name="tmean">
     <attributes>
       <attribute name="Conventions" value="CF-1.6"/>
       <attribute name="Note" value="This dataset is for test purposes only"/>
diff --git a/lib/iris/tests/results/pp_rules/global.cml b/lib/iris/tests/results/pp_rules/global.cml
index 2779549286..ad7063d025 100644
--- a/lib/iris/tests/results/pp_rules/global.cml
+++ b/lib/iris/tests/results/pp_rules/global.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="9999.0" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/pp_rules/lbproc_mean_max_min.cml b/lib/iris/tests/results/pp_rules/lbproc_mean_max_min.cml
index 1d8f73a624..00dc804914 100644
--- a/lib/iris/tests/results/pp_rules/lbproc_mean_max_min.cml
+++ b/lib/iris/tests/results/pp_rules/lbproc_mean_max_min.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -37,7 +37,7 @@
     <cellMethods/>
     <data checksum="0x80e93a14" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -78,7 +78,7 @@
     </cellMethods>
     <data checksum="0x85641c30" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -119,7 +119,7 @@
     </cellMethods>
     <data checksum="0x03d5c2e9" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -160,7 +160,7 @@
     </cellMethods>
     <data checksum="0xac9bd3e8" dtype="float32" shape="(145, 192)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/pp_rules/lbtim_2.cml b/lib/iris/tests/results/pp_rules/lbtim_2.cml
index 8ff9abfd72..868ce81e7d 100644
--- a/lib/iris/tests/results/pp_rules/lbtim_2.cml
+++ b/lib/iris/tests/results/pp_rules/lbtim_2.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/pp_rules/ocean_depth.cml b/lib/iris/tests/results/pp_rules/ocean_depth.cml
index 7e71f6f20e..7cbafa6cd4 100644
--- a/lib/iris/tests/results/pp_rules/ocean_depth.cml
+++ b/lib/iris/tests/results/pp_rules/ocean_depth.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="sea_water_potential_temperature" units="degC">
+  <cube core-dtype="float32" dtype="float32" standard_name="sea_water_potential_temperature" units="degC">
     <attributes>
       <attribute name="STASH" value="m02s00i101"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/pp_rules/ocean_depth_bounded.cml b/lib/iris/tests/results/pp_rules/ocean_depth_bounded.cml
index f237523131..3aee7ff671 100644
--- a/lib/iris/tests/results/pp_rules/ocean_depth_bounded.cml
+++ b/lib/iris/tests/results/pp_rules/ocean_depth_bounded.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="sea_water_potential_temperature" units="degC">
+  <cube core-dtype="float32" dtype="float32" standard_name="sea_water_potential_temperature" units="degC">
     <attributes>
       <attribute name="STASH" value="m02s00i101"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/pp_rules/rotated_uk.cml b/lib/iris/tests/results/pp_rules/rotated_uk.cml
index e4cbe096da..5ad678c9b9 100644
--- a/lib/iris/tests/results/pp_rules/rotated_uk.cml
+++ b/lib/iris/tests/results/pp_rules/rotated_uk.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="wind_speed_of_gust" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="wind_speed_of_gust" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s03i463"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/regrid/airpress_on_theta_0d.cml b/lib/iris/tests/results/regrid/airpress_on_theta_0d.cml
index c7385cb73d..8b52a0eb80 100644
--- a/lib/iris/tests/results/regrid/airpress_on_theta_0d.cml
+++ b/lib/iris/tests/results/regrid/airpress_on_theta_0d.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s00i408"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/regrid/airpress_on_theta_1d.cml b/lib/iris/tests/results/regrid/airpress_on_theta_1d.cml
index 5578685dba..4f91acd589 100644
--- a/lib/iris/tests/results/regrid/airpress_on_theta_1d.cml
+++ b/lib/iris/tests/results/regrid/airpress_on_theta_1d.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s00i408"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/regrid/airpress_on_theta_2d.cml b/lib/iris/tests/results/regrid/airpress_on_theta_2d.cml
index fac981fc3a..d73d0c4430 100644
--- a/lib/iris/tests/results/regrid/airpress_on_theta_2d.cml
+++ b/lib/iris/tests/results/regrid/airpress_on_theta_2d.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s00i408"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/regrid/airpress_on_theta_3d.cml b/lib/iris/tests/results/regrid/airpress_on_theta_3d.cml
index b282aade93..d8dc722cec 100644
--- a/lib/iris/tests/results/regrid/airpress_on_theta_3d.cml
+++ b/lib/iris/tests/results/regrid/airpress_on_theta_3d.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_pressure" units="Pa">
     <attributes>
       <attribute name="STASH" value="m01s00i408"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/regrid/theta_on_airpress_0d.cml b/lib/iris/tests/results/regrid/theta_on_airpress_0d.cml
index 14bb6c0b45..380dc48af7 100644
--- a/lib/iris/tests/results/regrid/theta_on_airpress_0d.cml
+++ b/lib/iris/tests/results/regrid/theta_on_airpress_0d.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/regrid/theta_on_airpress_1d.cml b/lib/iris/tests/results/regrid/theta_on_airpress_1d.cml
index 6927fcfc0b..c1357d7b0a 100644
--- a/lib/iris/tests/results/regrid/theta_on_airpress_1d.cml
+++ b/lib/iris/tests/results/regrid/theta_on_airpress_1d.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/regrid/theta_on_airpress_2d.cml b/lib/iris/tests/results/regrid/theta_on_airpress_2d.cml
index 213c07a6e8..cf04c386e7 100644
--- a/lib/iris/tests/results/regrid/theta_on_airpress_2d.cml
+++ b/lib/iris/tests/results/regrid/theta_on_airpress_2d.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/regrid/theta_on_airpress_3d.cml b/lib/iris/tests/results/regrid/theta_on_airpress_3d.cml
index ce4db59a32..65d19cf14e 100644
--- a/lib/iris/tests/results/regrid/theta_on_airpress_3d.cml
+++ b/lib/iris/tests/results/regrid/theta_on_airpress_3d.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/system/supported_filetype_.pp.cml b/lib/iris/tests/results/system/supported_filetype_.pp.cml
index ff3192275a..80bd5e704b 100644
--- a/lib/iris/tests/results/system/supported_filetype_.pp.cml
+++ b/lib/iris/tests/results/system/supported_filetype_.pp.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="wind_speed" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="wind_speed" units="m s-1">
     <coords>
       <coord>
         <dimCoord id="1d45e087" points="[9.0]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="float64"/>
diff --git a/lib/iris/tests/results/trajectory/constant_latitude.cml b/lib/iris/tests/results/trajectory/constant_latitude.cml
index 22f31e282e..b3bb8a4257 100644
--- a/lib/iris/tests/results/trajectory/constant_latitude.cml
+++ b/lib/iris/tests/results/trajectory/constant_latitude.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/trajectory/single_point.cml b/lib/iris/tests/results/trajectory/single_point.cml
index 92f333d984..7b2b3293d5 100644
--- a/lib/iris/tests/results/trajectory/single_point.cml
+++ b/lib/iris/tests/results/trajectory/single_point.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/trajectory/tri_polar_latitude_slice.cml b/lib/iris/tests/results/trajectory/tri_polar_latitude_slice.cml
index 667cc75881..cf5d676534 100644
--- a/lib/iris/tests/results/trajectory/tri_polar_latitude_slice.cml
+++ b/lib/iris/tests/results/trajectory/tri_polar_latitude_slice.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="9.96920996839e+36" long_name="Temperature" standard_name="sea_water_potential_temperature" units="degC" var_name="votemper">
+  <cube core-dtype="float64" dtype="float64" long_name="Temperature" standard_name="sea_water_potential_temperature" units="degC" var_name="votemper">
     <attributes>
       <attribute name="Conventions" value="CF-1.1"/>
       <attribute name="DOMAIN_DIM_N001" value="x"/>
diff --git a/lib/iris/tests/results/trajectory/zigzag.cml b/lib/iris/tests/results/trajectory/zigzag.cml
index 00a2b214ec..46fb640969 100644
--- a/lib/iris/tests/results/trajectory/zigzag.cml
+++ b/lib/iris/tests/results/trajectory/zigzag.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float64" dtype="float64" standard_name="air_potential_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s00i004"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/uri_callback/pp_global.cml b/lib/iris/tests/results/uri_callback/pp_global.cml
index ce1867b078..90a3efe009 100644
--- a/lib/iris/tests/results/uri_callback/pp_global.cml
+++ b/lib/iris/tests/results/uri_callback/pp_global.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="filename" value="global.pp"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/001000000000.00.000.000000.1860.01.01.00.00.f.b_0.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/001000000000.00.000.000000.1860.01.01.00.00.f.b_0.cml
index 3bbce1c88a..602a4c2563 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/001000000000.00.000.000000.1860.01.01.00.00.f.b_0.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/001000000000.00.000.000000.1860.01.01.00.00.f.b_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="sea_surface_height_above_geoid" units="m" var_name="sea_surface_height_above_geoid">
+  <cube core-dtype="float32" dtype="float32" standard_name="sea_surface_height_above_geoid" units="m" var_name="sea_surface_height_above_geoid">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
     </attributes>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/002000000000.44.101.131200.1920.09.01.00.00.b_0.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/002000000000.44.101.131200.1920.09.01.00.00.b_0.cml
index 7d36670817..8dbbc28f0a 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/002000000000.44.101.131200.1920.09.01.00.00.b_0.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/002000000000.44.101.131200.1920.09.01.00.00.b_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="1" var_name="unknown">
+  <cube core-dtype="float32" dtype="float32" units="1" var_name="unknown">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
       <attribute name="STASH" value="m??s44i101"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/ocean_xsect.b_0.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/ocean_xsect.b_0.cml
index 2cb6add07f..320fb0f500 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/ocean_xsect.b_0.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/ocean_xsect.b_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="sea_water_potential_temperature" units="degC" var_name="sea_water_potential_temperature">
+  <cube core-dtype="float32" dtype="float32" standard_name="sea_water_potential_temperature" units="degC" var_name="sea_water_potential_temperature">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
       <attribute name="STASH" value="m02s00i101"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st0fc699.b_0.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st0fc699.b_0.cml
index 0188278080..693ad593c8 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st0fc699.b_0.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st0fc699.b_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="1" var_name="unknown">
+  <cube core-dtype="float32" dtype="float32" units="1" var_name="unknown">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
       <attribute name="STASH" value="m02s00i???"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st0fc942.b_0.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st0fc942.b_0.cml
index 2737aef8a8..82d8bfe47c 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st0fc942.b_0.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st0fc942.b_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="1" var_name="unknown">
+  <cube core-dtype="float32" dtype="float32" units="1" var_name="unknown">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
       <attribute name="STASH" value="m02s00i???"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st30211.b_0.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st30211.b_0.cml
index 9d5a2963e1..ea42daee37 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st30211.b_0.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_netcdf/st30211.b_0.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="northward_ocean_heat_transport" units="PW" var_name="northward_ocean_heat_transport">
+  <cube core-dtype="float32" dtype="float32" standard_name="northward_ocean_heat_transport" units="PW" var_name="northward_ocean_heat_transport">
     <attributes>
       <attribute name="Conventions" value="CF-1.5"/>
       <attribute name="STASH" value="m02s30i211"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.000128.1990.12.01.00.00.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.000128.1990.12.01.00.00.b.cml
index 7c7fd73071..d86da5d7f0 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.000128.1990.12.01.00.00.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.000128.1990.12.01.00.00.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.004224.1990.12.01.00.00.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.004224.1990.12.01.00.00.b.cml
index 3e1c4e410d..9721c1c337 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.004224.1990.12.01.00.00.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.004224.1990.12.01.00.00.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.008320.1990.12.01.00.00.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.008320.1990.12.01.00.00.b.cml
index 0add047cb5..9b8099f0d3 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.008320.1990.12.01.00.00.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.03.236.008320.1990.12.01.00.00.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.16.202.000128.1860.09.01.00.00.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.16.202.000128.1860.09.01.00.00.b.cml
index 00228b6062..9996a29982 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.16.202.000128.1860.09.01.00.00.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/000003000000.16.202.000128.1860.09.01.00.00.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="geopotential_height" units="m">
+  <cube core-dtype="float32" dtype="float32" standard_name="geopotential_height" units="m">
     <attributes>
       <attribute name="STASH" value="m01s16i202"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/001000000000.00.000.000000.1860.01.01.00.00.f.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/001000000000.00.000.000000.1860.01.01.00.00.f.b.cml
index 3eb9c511fc..19036efc41 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/001000000000.00.000.000000.1860.01.01.00.00.f.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/001000000000.00.000.000000.1860.01.01.00.00.f.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="sea_surface_height_above_geoid" units="m">
+  <cube core-dtype="float32" dtype="float32" standard_name="sea_surface_height_above_geoid" units="m">
     <coords>
       <coord>
         <dimCoord bounds="[[-86400.0, 0.0]]" id="1d45e087" points="[-43200.0]" shape="(1,)" standard_name="forecast_period" units="Unit('hours')" value_type="float64"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/002000000000.44.101.131200.1920.09.01.00.00.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/002000000000.44.101.131200.1920.09.01.00.00.b.cml
index a7c05c68d4..423aed112d 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/002000000000.44.101.131200.1920.09.01.00.00.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/002000000000.44.101.131200.1920.09.01.00.00.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="unknown">
+  <cube core-dtype="float32" dtype="float32" units="unknown">
     <attributes>
       <attribute name="STASH" value="m??s44i101"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/008000000000.44.101.000128.1890.09.01.00.00.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/008000000000.44.101.000128.1890.09.01.00.00.b.cml
index 172795a587..02cc81bf6b 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/008000000000.44.101.000128.1890.09.01.00.00.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/008000000000.44.101.000128.1890.09.01.00.00.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="unknown">
+  <cube core-dtype="float32" dtype="float32" units="unknown">
     <attributes>
       <attribute name="STASH" value="m??s44i101"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/12187.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/12187.b.cml
index abe280a915..e1be4ef2c0 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/12187.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/12187.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" long_name="change_over_time_in_upward_air_velocity_due_to_advection" units="m s-1">
+  <cube core-dtype="float32" dtype="float32" long_name="change_over_time_in_upward_air_velocity_due_to_advection" units="m s-1">
     <attributes>
       <attribute name="STASH" value="m01s12i187"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/HadCM2_ts_SAT_ann_18602100.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/HadCM2_ts_SAT_ann_18602100.b.cml
index 41c1b7581c..ec16f05cf0 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/HadCM2_ts_SAT_ann_18602100.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/HadCM2_ts_SAT_ann_18602100.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="Celsius">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="Celsius">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_level_lat_orig.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_level_lat_orig.b.cml
index 65dda30cc7..d1e1bef60e 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_level_lat_orig.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_level_lat_orig.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="geopotential_height" units="m">
+  <cube core-dtype="float32" dtype="float32" standard_name="geopotential_height" units="m">
     <attributes>
       <attribute name="STASH" value="m01s16i202"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_lon_lat_press_orig.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_lon_lat_press_orig.b.cml
index 8b73a8db3a..182f9c96ff 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_lon_lat_press_orig.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_lon_lat_press_orig.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="geopotential_height" units="m">
+  <cube core-dtype="float32" dtype="float32" standard_name="geopotential_height" units="m">
     <attributes>
       <attribute name="STASH" value="m01s16i202"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_lon_lat_several.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_lon_lat_several.b.cml
index 9ee5e5d275..1553ac9f23 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_lon_lat_several.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_lon_lat_several.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_n10r13xy.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_n10r13xy.b.cml
index b24f67bb2f..03dc8a7659 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_n10r13xy.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_n10r13xy.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="source" value="Data from Met Office Unified Model"/>
     </attributes>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_time_press.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_time_press.b.cml
index 64efb9da32..95177cd0b4 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_time_press.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_time_press.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="geopotential_height" units="m">
+  <cube core-dtype="float32" dtype="float32" standard_name="geopotential_height" units="m">
     <attributes>
       <attribute name="STASH" value="m01s16i202"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_tseries.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_tseries.b.cml
index 6bfad0dad3..77025cc627 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_tseries.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/aaxzc_tseries.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/abcza_pa19591997_daily_29.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/abcza_pa19591997_daily_29.b.cml
index 6f9491951c..d67206b642 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/abcza_pa19591997_daily_29.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/abcza_pa19591997_daily_29.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -63,7 +63,7 @@
     </cellMethods>
     <data checksum="0x82b10a0a" dtype="float32" shape="(360, 73, 96)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s03i236"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
@@ -126,7 +126,7 @@
     </cellMethods>
     <data checksum="0xd9f6eff7" dtype="float32" shape="(360, 73, 96)"/>
   </cube>
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="precipitation_flux" units="kg m-2 s-1">
+  <cube core-dtype="float32" dtype="float32" standard_name="precipitation_flux" units="kg m-2 s-1">
     <attributes>
       <attribute name="STASH" value="m01s05i216"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/abxpa_press_lat.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/abxpa_press_lat.b.cml
index 6fb4c3fe64..227eca3abd 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/abxpa_press_lat.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/abxpa_press_lat.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" standard_name="geopotential_height" units="m">
+  <cube core-dtype="float32" dtype="float32" standard_name="geopotential_height" units="m">
     <attributes>
       <attribute name="STASH" value="m01s16i202"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/model.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/model.b.cml
index 9ba807ca0c..0a0c72caea 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/model.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/model.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" standard_name="air_temperature" units="K">
     <attributes>
       <attribute name="STASH" value="m01s16i203"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/ocean_xsect.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/ocean_xsect.b.cml
index 5ec956458e..c22fc8c248 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/ocean_xsect.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/ocean_xsect.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="sea_water_potential_temperature" units="degC">
+  <cube core-dtype="float32" dtype="float32" standard_name="sea_water_potential_temperature" units="degC">
     <attributes>
       <attribute name="STASH" value="m02s00i101"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st0fc699.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st0fc699.b.cml
index 974426afc9..338e5c69bd 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st0fc699.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st0fc699.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="unknown">
+  <cube core-dtype="float32" dtype="float32" units="unknown">
     <attributes>
       <attribute name="STASH" value="m02s00i???"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st0fc942.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st0fc942.b.cml
index cd2cf478dc..7c73cfbe87 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st0fc942.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st0fc942.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" units="unknown">
+  <cube core-dtype="float32" dtype="float32" units="unknown">
     <attributes>
       <attribute name="STASH" value="m02s00i???"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st30211.b.cml b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st30211.b.cml
index 230f890423..e0547febdd 100644
--- a/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st30211.b.cml
+++ b/lib/iris/tests/results/usecases/pp_to_cf_conversion/from_pp/st30211.b.cml
@@ -1,6 +1,6 @@
 <?xml version="1.0" ?>
 <cubes xmlns="urn:x-iris:cubeml-0.2">
-  <cube core-dtype="float32" dtype="float32" fill_value="-1e+30" standard_name="northward_ocean_heat_transport" units="PW">
+  <cube core-dtype="float32" dtype="float32" standard_name="northward_ocean_heat_transport" units="PW">
     <attributes>
       <attribute name="STASH" value="m02s30i211"/>
       <attribute name="source" value="Data from Met Office Unified Model"/>
diff --git a/lib/iris/tests/test_analysis.py b/lib/iris/tests/test_analysis.py
index 0ffd7e18ab..091670972b 100644
--- a/lib/iris/tests/test_analysis.py
+++ b/lib/iris/tests/test_analysis.py
@@ -129,13 +129,13 @@ def test_weighted_mean_little(self):
         # to catch cases where there is a loss of precision however.
         if a.dtype > np.float32:
             cast_data = a.data.astype(np.float32)
-            a.replace(cast_data, fill_value=a.fill_value)
+            a.data = cast_data
         self.assertCMLApproxData(a, ('analysis', 'weighted_mean_lat.cml'))
 
         b = cube.collapsed(lon_coord, iris.analysis.MEAN, weights=weights)
         if b.dtype > np.float32:
             cast_data = b.data.astype(np.float32)
-            b.replace(cast_data, fill_value=b.fill_value)
+            b.data = cast_data
         b.data = np.asarray(b.data)
         self.assertCMLApproxData(b, ('analysis', 'weighted_mean_lon.cml'))
         self.assertEqual(b.coord('dummy').shape, (1, ))
@@ -144,7 +144,7 @@ def test_weighted_mean_little(self):
         c = cube.collapsed([lat_coord[:], lon_coord], iris.analysis.MEAN, weights=weights)
         if c.dtype > np.float32:
             cast_data = c.data.astype(np.float32)
-            c.replace(cast_data, fill_value=c.fill_value)
+            c.data = cast_data
         self.assertCMLApproxData(c, ('analysis', 'weighted_mean_latlon.cml'))
         self.assertEqual(c.coord('dummy').shape, (1, ))
 
@@ -205,12 +205,10 @@ def setUp(self):
         file = tests.get_data_path(('PP', 'aPProt1', 'rotatedMHtimecube.pp'))
         cubes = iris.load(file)
         self.cube = cubes[0]
-        self.cube_fill_val = self.cube.fill_value
         self.assertCML(self.cube, ('analysis', 'original.cml'))
 
     def _common(self, name, aggregate, original_name='original_common.cml', *args, **kwargs):
         self.cube.data = self.cube.data.astype(np.float64)
-        self.cube.fill_value = self.cube_fill_val
 
         self.assertCML(self.cube, ('analysis', original_name))
 
@@ -236,7 +234,6 @@ def test_std_dev(self):
     def test_hmean(self):
         # harmonic mean requires data > 0
         self.cube.data *= self.cube.data
-        self.cube.fill_value = self.cube_fill_val
         self._common('hmean', iris.analysis.HMEAN, 'original_hmean.cml', rtol=1e-05)
 
     def test_gmean(self):
diff --git a/lib/iris/tests/test_basic_maths.py b/lib/iris/tests/test_basic_maths.py
index 9d9dc195d4..ca15dea4b1 100644
--- a/lib/iris/tests/test_basic_maths.py
+++ b/lib/iris/tests/test_basic_maths.py
@@ -39,8 +39,7 @@
 class TestBasicMaths(tests.IrisTest):
     def setUp(self):
         self.cube = iris.tests.stock.global_pp()
-        self.cube.replace(self.cube.data - 260,
-                          fill_value=self.cube.fill_value)
+        self.cube.data = self.cube.data - 260
 
     def test_abs(self):
         a = self.cube
@@ -361,11 +360,7 @@ def test_type_error(self):
 class TestDivideAndMultiply(tests.IrisTest):
     def setUp(self):
         self.cube = iris.tests.stock.global_pp()
-        # We require to preserve the cube fill_value
-        # across the cube data setter operation.
-        fill_value = self.cube.fill_value
         self.cube.data = self.cube.data - 260
-        self.cube.fill_value = fill_value
 
     def test_divide(self):
         a = self.cube
@@ -499,17 +494,11 @@ def test_multiplication_not_in_place(self):
 class TestExponentiate(tests.IrisTest):
     def setUp(self):
         self.cube = iris.tests.stock.global_pp()
-        # We require to preserve the cube fill_value
-        # across the cube data setter operation.
-        self.fill_value = self.cube.fill_value
         self.cube.data = self.cube.data - 260
-        self.cube.fill_value = self.fill_value
 
     def test_exponentiate(self):
         a = self.cube
         a.data = a.data.astype(np.float64)
-        # We require to preserve the cube fill_value after setting the data.
-        a.fill_value = self.fill_value
         e = pow(a, 4)
         self.assertCMLApproxData(e, ('analysis', 'exponentiate.cml'))
 
@@ -517,8 +506,6 @@ def test_square_root(self):
         # Make sure we have something which we can take the root of.
         a = self.cube
         a.data = abs(a.data)
-        # We require to preserve the cube fill_value after setting the data.
-        a.fill_value = self.fill_value
         a.units **= 2
 
         e = a ** 0.5
diff --git a/lib/iris/tests/test_cdm.py b/lib/iris/tests/test_cdm.py
index 1e03bdfbf4..9e12c91f08 100644
--- a/lib/iris/tests/test_cdm.py
+++ b/lib/iris/tests/test_cdm.py
@@ -1030,13 +1030,13 @@ def collapse_test_common(self, cube, a_name, b_name, *args, **kwargs):
         # want to catch cases where there is a loss of precision however.
         if dual_stage.dtype > cube.dtype:
             data = dual_stage.data.astype(cube.dtype)
-            dual_stage.replace(data, fill_value=dual_stage.fill_value)
+            dual_stage.data = data
         self.assertCMLApproxData(dual_stage, ('cube_collapsed', '%s_%s_dual_stage.cml' % (a_filename, b_filename)), *args, **kwargs)
 
         single_stage = cube.collapsed([a_name, b_name], iris.analysis.MEAN)
         if single_stage.dtype > cube.dtype:
             data = single_stage.data.astype(cube.dtype)
-            single_stage.replace(data, fill_value=single_stage.fill_value)
+            single_stage.data = data
         self.assertCMLApproxData(single_stage, ('cube_collapsed', '%s_%s_single_stage.cml' % (a_filename, b_filename)), *args, **kwargs)
 
         # Compare the cube bits that should match
@@ -1199,7 +1199,6 @@ def test_save_and_merge(self):
             self.assertEqual(len(merged_cubes), 1, "expected a single merged cube")
             merged_cube = merged_cubes[0]
             self.assertEqual(merged_cube.dtype, dtype)
-            self.assertEqual(merged_cube.fill_value, fill_value)
 
 
 @tests.skip_data
diff --git a/lib/iris/tests/test_concatenate.py b/lib/iris/tests/test_concatenate.py
index ee03370509..c00360d887 100644
--- a/lib/iris/tests/test_concatenate.py
+++ b/lib/iris/tests/test_concatenate.py
@@ -94,7 +94,7 @@ def _make_cube(x, y, data, aux=None, offset=0, scalar=None,
         cube_data = np.empty(shape, dtype=dtype)
         cube_data[:] = data
 
-    cube = iris.cube.Cube(cube_data, fill_value=fill_value)
+    cube = iris.cube.Cube(cube_data)
     coord = DimCoord(y_range, long_name='y')
     coord.guess_bounds()
     cube.add_dim_coord(coord, 0)
@@ -233,18 +233,12 @@ def concatenate(cubes, order=None):
     result = cubelist.concatenate()
 
     for cube in result:
-        # Setting the cube.data clears the cube.dtype and cube.fill_value.
-        # We want to maintain the fill_value for testing purposes, even
-        # though we have lost the lazy data in order to pin down the array
-        # data order to overcome testing on different architectures.
-        fill_value = cube.fill_value
         if ma.isMaskedArray(cube.data):
             data = np.array(cube.data.data, copy=True, order=order)
             mask = np.array(cube.data.mask, copy=True, order=order)
             cube.data = ma.array(data, mask=mask)
         else:
             cube.data = np.array(cube.data, copy=True, order=order)
-        cube.fill_value = fill_value
 
     return result
 
@@ -347,7 +341,6 @@ def test_masked_and_unmasked__default_fill_value(self):
         cubes.append(_make_cube((2, 4), y, 2))
         result = concatenate(cubes)
         self.assertEqual(len(result), 1)
-        self.assertIsNone(result[0].fill_value)
         np_fill_value = ma.masked_array(0, dtype=result[0].dtype).fill_value
         self.assertEqual(result[0].data.fill_value, np_fill_value)
 
@@ -359,7 +352,6 @@ def test_unmasked_and_masked__default_fill_value(self):
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertEqual(len(result), 1)
-        self.assertIsNone(result[0].fill_value)
         np_fill_value = ma.masked_array(0, dtype=result[0].dtype).fill_value
         self.assertEqual(result[0].data.fill_value, np_fill_value)
 
@@ -374,7 +366,6 @@ def test_masked_and_unmasked__fill_value_equal(self):
                                 fill_value=fill_value))
         result = concatenate(cubes)
         self.assertEqual(len(result), 1)
-        self.assertEqual(result[0].fill_value, fill_value)
         self.assertEqual(result[0].data.fill_value, fill_value)
 
     def test_masked_and_unmasked_int16__fill_value_equal(self):
@@ -389,7 +380,6 @@ def test_masked_and_unmasked_int16__fill_value_equal(self):
                                 fill_value=fill_value))
         result = concatenate(cubes)
         self.assertEqual(len(result), 1)
-        self.assertEqual(result[0].fill_value, fill_value)
         self.assertEqual(result[0].data.fill_value, fill_value)
 
     def test_unmasked_and_masked__default_fill_value_from_None(self):
@@ -401,7 +391,6 @@ def test_unmasked_and_masked__default_fill_value_from_None(self):
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertEqual(len(result), 1)
-        self.assertIsNone(result[0].fill_value)
         np_fill_value = ma.masked_array(0, dtype=result[0].dtype).fill_value
         self.assertEqual(result[0].data.fill_value, np_fill_value)
 
@@ -415,7 +404,6 @@ def test_unmasked_and_masked_int16__default_fill_value_from_diff(self):
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertEqual(len(result), 1)
-        self.assertIsNone(result[0].fill_value)
         np_fill_value = ma.masked_array(0, dtype=result[0].dtype).fill_value
         self.assertEqual(result[0].data.fill_value, np_fill_value)
 
@@ -437,7 +425,6 @@ def test_masked_with_data_fill_value_difference_on_arrays(self):
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertEqual(len(result), 1)
-        self.assertEqual(result[0].fill_value, fill_value)
         self.assertEqual(result[0].data.fill_value, fill_value)
 
     def test_concat_masked_2x2d__default_fill_value_from_None(self):
@@ -456,7 +443,6 @@ def test_concat_masked_2x2d__default_fill_value_from_None(self):
         mask = np.array([[True, False, False, True],
                          [False, True, True, False]], dtype=np.bool)
         self.assertArrayEqual(result[0].data.mask, mask)
-        self.assertIsNone(result[0].fill_value)
         np_fill_value = ma.masked_array(0, dtype=result[0].dtype).fill_value
         self.assertEqual(result[0].data.fill_value, np_fill_value)
 
@@ -478,7 +464,6 @@ def test_concat_masked_2y2d__default_fill_value_from_diff(self):
                          [False, True],
                          [True, False]], dtype=np.bool)
         self.assertArrayEqual(result[0].data.mask, mask)
-        self.assertIsNone(result[0].fill_value)
         np_fill_value = ma.masked_array(0, dtype=result[0].dtype).fill_value
         self.assertEqual(result[0].data.fill_value, np_fill_value)
 
@@ -504,7 +489,6 @@ def test_concat_masked_2y2d_int16(self):
                          [False, True],
                          [True, False]], dtype=np.bool)
         self.assertArrayEqual(result[0].data.mask, mask)
-        self.assertEqual(result[0].fill_value, fill_value)
         self.assertEqual(result[0].data.fill_value, fill_value)
 
     def test_concat_masked_2y2d_int16_with_concrete_and_lazy(self):
@@ -518,7 +502,7 @@ def test_concat_masked_2y2d_int16_with_concrete_and_lazy(self):
         cubes.append(cube)
         mask = [(0, 1), (1, 0)]
         cube = _make_cube(x, (2, 4), 2, dtype=dtype, mask=mask)
-        cube.replace(cube.lazy_data(), dtype=dtype, fill_value=fill_value)
+        cube.data = cube.lazy_data()
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertCML(result, ('concatenate', 'concat_masked_2y2d_int16.cml'))
@@ -529,7 +513,6 @@ def test_concat_masked_2y2d_int16_with_concrete_and_lazy(self):
                          [False, True],
                          [True, False]], dtype=np.bool)
         self.assertArrayEqual(result[0].data.mask, mask)
-        self.assertEqual(result[0].fill_value, fill_value)
         self.assertEqual(result[0].data.fill_value, fill_value)
 
     def test_concat_masked_2y2d_int16_with_lazy_and_concrete(self):
@@ -539,7 +522,7 @@ def test_concat_masked_2y2d_int16_with_lazy_and_concrete(self):
         fill_value = -37
         mask = [(0, 1), (1, 0)]
         cube = _make_cube(x, (2, 4), 2, dtype=dtype, mask=mask)
-        cube.replace(cube.lazy_data(), dtype=dtype, fill_value=fill_value)
+        cube.data = cube.lazy_data()
         cubes.append(cube)
         mask = [(0, 1), (0, 1)]
         cube = _make_cube(x, (0, 2), 1, dtype=dtype, mask=mask,
@@ -554,7 +537,6 @@ def test_concat_masked_2y2d_int16_with_lazy_and_concrete(self):
                          [False, True],
                          [True, False]], dtype=np.bool)
         self.assertArrayEqual(result[0].data.mask, mask)
-        self.assertEqual(result[0].fill_value, fill_value)
         self.assertEqual(result[0].data.fill_value, fill_value)
 
     def test_concat_2x2d__default_fill_value(self):
@@ -566,7 +548,6 @@ def test_concat_2x2d__default_fill_value(self):
         self.assertCML(result, ('concatenate', 'concat_2x2d.cml'))
         self.assertEqual(len(result), 1)
         self.assertEqual(result[0].shape, (2, 6))
-        self.assertIsNone(result[0].fill_value)
 
     def test_concat_2y2d__fill_value_equal(self):
         cubes = []
@@ -578,7 +559,6 @@ def test_concat_2y2d__fill_value_equal(self):
         self.assertCML(result, ('concatenate', 'concat_2y2d.cml'))
         self.assertEqual(len(result), 1)
         self.assertEqual(result[0].shape, (6, 2))
-        self.assertEqual(result[0].fill_value, fill_value)
 
     def test_concat_2x2d_aux_x__default_fill_value_from_diff(self):
         cubes = []
@@ -589,7 +569,6 @@ def test_concat_2x2d_aux_x__default_fill_value_from_diff(self):
         self.assertCML(result, ('concatenate', 'concat_2x2d_aux_x.cml'))
         self.assertEqual(len(result), 1)
         self.assertEqual(result[0].shape, (2, 6))
-        self.assertIsNone(result[0].fill_value)
 
     def test_concat_2y2d_aux_x__default_fill_value_from_diff(self):
         cubes = []
@@ -600,7 +579,6 @@ def test_concat_2y2d_aux_x__default_fill_value_from_diff(self):
         self.assertCML(result, ('concatenate', 'concat_2y2d_aux_x.cml'))
         self.assertEqual(len(result), 1)
         self.assertEqual(result[0].shape, (6, 2))
-        self.assertIsNone(result[0].fill_value)
 
     def test_concat_2x2d_aux_y(self):
         cubes = []
@@ -767,7 +745,6 @@ def test_fill_value_invariant_to_order__same_non_None(self):
                             fill_value=fill_value) for i in range(3)]
         for combo in itertools.permutations(cubes):
             result = iris.cube.CubeList(combo).concatenate_cube()
-            self.assertEqual(result.fill_value, fill_value)
             self.assertEqual(result.data.fill_value, fill_value)
 
     def test_fill_value_invariant_to_order__all_None(self):
@@ -776,7 +753,6 @@ def test_fill_value_invariant_to_order__all_None(self):
                             fill_value=None) for i in range(3)]
         for combo in itertools.permutations(cubes):
             result = iris.cube.CubeList(combo).concatenate_cube()
-            self.assertIsNone(result.fill_value)
             np_fill_value = ma.masked_array(0, dtype=result.dtype).fill_value
             self.assertEqual(result.data.fill_value, np_fill_value)
 
@@ -788,7 +764,6 @@ def test_fill_value_invariant_to_order__different_non_None(self):
         cubes.append(_make_cube((6, 8), y, 3, mask=True, fill_value=4123))
         for combo in itertools.permutations(cubes):
             result = iris.cube.CubeList(combo).concatenate_cube()
-            self.assertIsNone(result.fill_value)
             np_fill_value = ma.masked_array(0, dtype=result.dtype).fill_value
             self.assertEqual(result.data.fill_value, np_fill_value)
 
@@ -799,7 +774,6 @@ def test_fill_value_invariant_to_order__mixed(self):
         cubes.append(_make_cube((4, 6), y, 2, mask=True, fill_value=4321))
         for combo in itertools.permutations(cubes):
             result = iris.cube.CubeList(combo).concatenate_cube()
-            self.assertIsNone(result.fill_value)
             np_fill_value = ma.masked_array(0, dtype=result.dtype).fill_value
             self.assertEqual(result.data.fill_value, np_fill_value)
 
diff --git a/lib/iris/tests/test_interpolation.py b/lib/iris/tests/test_interpolation.py
index 9880c6add6..78862ab4b5 100644
--- a/lib/iris/tests/test_interpolation.py
+++ b/lib/iris/tests/test_interpolation.py
@@ -42,8 +42,7 @@ def normalise_order(cube):
     #     function when the circular flag is true.
     #   * scipy.interpolate.interp1d in 0.11.0 which is used in
     #     `Linear1dExtrapolator`.
-    data = np.ascontiguousarray(cube.data)
-    cube.replace(data, fill_value=cube.fill_value)
+    cube.data = np.ascontiguousarray(cube.data)
 
 
 class TestLinearExtrapolator(tests.IrisTest):
diff --git a/lib/iris/tests/test_merge.py b/lib/iris/tests/test_merge.py
index 328f902ce2..7fc693bb06 100644
--- a/lib/iris/tests/test_merge.py
+++ b/lib/iris/tests/test_merge.py
@@ -136,7 +136,7 @@ def _make_cube(self, data, dtype=np.dtype('int32'), fill_value=None,
         y = np.arange(N)
         payload = self._make_data(data, dtype=dtype, fill_value=fill_value,
                                   mask=mask, lazy=lazy, N=N)
-        cube = iris.cube.Cube(payload, dtype=dtype, fill_value=fill_value)
+        cube = iris.cube.Cube(payload)
         lat = DimCoord(y, standard_name='latitude', units='degrees')
         cube.add_dim_coord(lat, 0)
         lon = DimCoord(x, standard_name='longitude', units='degrees')
@@ -155,14 +155,12 @@ def _expected_fill_value(fill0, fill1):
     def _check_fill_value(self, result, fill0, fill1):
         expected_fill_value = self._expected_fill_value(fill0, fill1)
         if expected_fill_value is None:
-            self.assertIsNone(result.fill_value)
             data = result.data
             if ma.isMaskedArray(data):
                 np_fill_value = ma.masked_array(0,
                                                 dtype=result.dtype).fill_value
                 self.assertEqual(data.fill_value, np_fill_value)
         else:
-            self.assertEqual(result.fill_value, expected_fill_value)
             data = result.data
             if ma.isMaskedArray(data):
                 self.assertEqual(data.fill_value, expected_fill_value)
@@ -251,7 +249,6 @@ def test_fill_value_invariant_to_order__same_non_None(self):
                                  fill_value=fill_value) for i in range(3)]
         for combo in itertools.permutations(cubes):
             result = iris.cube.CubeList(combo).merge_cube()
-            self.assertEqual(result.fill_value, fill_value)
             self.assertEqual(result.data.fill_value, fill_value)
 
     def test_fill_value_invariant_to_order__all_None(self):
@@ -259,7 +256,6 @@ def test_fill_value_invariant_to_order__all_None(self):
                                  fill_value=None) for i in range(3)]
         for combo in itertools.permutations(cubes):
             result = iris.cube.CubeList(combo).merge_cube()
-            self.assertIsNone(result.fill_value)
             np_fill_value = ma.masked_array(0, dtype=result.dtype).fill_value
             self.assertEqual(result.data.fill_value, np_fill_value)
 
@@ -270,7 +266,6 @@ def test_fill_value_invariant_to_order__different_non_None(self):
         cubes.append(self._make_cube(3, mask=True, fill_value=4123))
         for combo in itertools.permutations(cubes):
             result = iris.cube.CubeList(combo).merge_cube()
-            self.assertIsNone(result.fill_value)
             np_fill_value = ma.masked_array(0, dtype=result.dtype).fill_value
             self.assertEqual(result.data.fill_value, np_fill_value)
 
@@ -280,7 +275,6 @@ def test_fill_value_invariant_to_order__mixed(self):
         cubes.append(self._make_cube(2, mask=True, fill_value=4321))
         for combo in itertools.permutations(cubes):
             result = iris.cube.CubeList(combo).merge_cube()
-            self.assertIsNone(result.fill_value)
             np_fill_value = ma.masked_array(0, dtype=result.dtype).fill_value
             self.assertEqual(result.data.fill_value, np_fill_value)
 
diff --git a/lib/iris/tests/unit/analysis/regrid/test_RectilinearRegridder.py b/lib/iris/tests/unit/analysis/regrid/test_RectilinearRegridder.py
index 9f968a9ed6..ca86e5cdd7 100644
--- a/lib/iris/tests/unit/analysis/regrid/test_RectilinearRegridder.py
+++ b/lib/iris/tests/unit/analysis/regrid/test_RectilinearRegridder.py
@@ -1263,7 +1263,7 @@ def test_circular_src__masked_missingmask(self):
         # instead of being an array.
         src = self.src
         src.coord('longitude').circular = True
-        src.replace(ma.MaskedArray(src.data), fill_value=src.fill_value)
+        src.data = ma.MaskedArray(src.data)
         self.assertEqual(src.data.mask, False)
         method_results = self._check_circular_results(src, 'missingmask')
         for method_result in method_results:
diff --git a/lib/iris/tests/unit/analysis/test_MEAN.py b/lib/iris/tests/unit/analysis/test_MEAN.py
index 6460137419..3d40e7eb5e 100644
--- a/lib/iris/tests/unit/analysis/test_MEAN.py
+++ b/lib/iris/tests/unit/analysis/test_MEAN.py
@@ -43,13 +43,13 @@ def setUp(self):
 
     def test_mdtol_default(self):
         agg = MEAN.lazy_aggregate(self.array, axis=self.axis)
-        masked_result = as_concrete_data(agg, nans_replacement=ma.masked)
+        masked_result = as_concrete_data(agg)
         self.assertMaskedArrayAlmostEqual(masked_result,
                                           self.expected_masked)
 
     def test_mdtol_below(self):
         agg = MEAN.lazy_aggregate(self.array, axis=self.axis, mdtol=0.3)
-        masked_result = as_concrete_data(agg, nans_replacement=ma.masked)
+        masked_result = as_concrete_data(agg)
         expected_masked = self.expected_masked
         expected_masked.mask = [False, True, True, True]
         self.assertMaskedArrayAlmostEqual(masked_result,
@@ -57,7 +57,7 @@ def test_mdtol_below(self):
 
     def test_mdtol_above(self):
         agg = MEAN.lazy_aggregate(self.array, axis=self.axis, mdtol=0.4)
-        masked_result = as_concrete_data(agg, nans_replacement=ma.masked)
+        masked_result = as_concrete_data(agg)
         self.assertMaskedArrayAlmostEqual(masked_result,
                                           self.expected_masked)
 
@@ -66,7 +66,7 @@ def test_multi_axis(self):
         collapse_axes = (0, 2)
         lazy_data = as_lazy_data(data)
         agg = MEAN.lazy_aggregate(lazy_data, axis=collapse_axes)
-        result = as_concrete_data(agg, nans_replacement=ma.masked)
+        result = as_concrete_data(agg)
         expected = np.mean(data, axis=collapse_axes)
         self.assertArrayAllClose(result, expected)
 
diff --git a/lib/iris/tests/unit/analysis/test_STD_DEV.py b/lib/iris/tests/unit/analysis/test_STD_DEV.py
index 3934a5a518..f745537def 100644
--- a/lib/iris/tests/unit/analysis/test_STD_DEV.py
+++ b/lib/iris/tests/unit/analysis/test_STD_DEV.py
@@ -37,7 +37,7 @@ def test_mdtol(self):
                           [1., 2., na, na]])
         array = as_lazy_data(array)
         var = STD_DEV.lazy_aggregate(array, axis=1, mdtol=0.3)
-        masked_result = as_concrete_data(var, nans_replacement=np.ma.masked)
+        masked_result = as_concrete_data(var)
         masked_expected = np.ma.masked_array([0.57735, 1., 0.707107],
                                              mask=[0, 0, 1])
         self.assertMaskedArrayAlmostEqual(masked_result, masked_expected)
diff --git a/lib/iris/tests/unit/cube/test_Cube.py b/lib/iris/tests/unit/cube/test_Cube.py
index 14dba07b85..19cf80a45d 100644
--- a/lib/iris/tests/unit/cube/test_Cube.py
+++ b/lib/iris/tests/unit/cube/test_Cube.py
@@ -1259,85 +1259,6 @@ def regridder(self, src, target):
         self.assertEqual(result, (scheme, cube, mock.sentinel.TARGET, cube))
 
 
-class Test_replace(tests.IrisTest):
-    def test(self):
-        cube = stock.simple_1d()
-        data = np.ones(cube.shape)
-        cube.replace(data)
-        self.assertIs(cube.core_data(), data)
-
-    def test__lazy(self):
-        cube = stock.simple_1d()
-        data = as_lazy_data(cube.data)
-        cube.replace(data)
-        self.assertIs(cube.core_data(), data)
-        self.assertTrue(cube.has_lazy_data())
-
-    def test__lazy_with_dtype_change(self):
-        lazy = as_lazy_data(np.array(10.0))
-        dtype = np.dtype('int16')
-        cube = Cube(lazy)
-        cube.replace(lazy * 10, dtype=dtype)
-        self.assertEqual(cube.dtype, dtype)
-        self.assertEqual(cube.core_data().dtype, lazy.dtype)
-
-    def test__lazy_masked_with_dtype_change(self):
-        real = ma.array(10)
-        real.mask = True
-        lazy = as_lazy_data(real)
-        dtype = np.dtype('int16')
-        cube = Cube(lazy, dtype=real.dtype)
-        self.assertEqual(cube.dtype, real.dtype)
-        self.assertEqual(cube.core_data().dtype, lazy.dtype)
-        cube.replace(lazy * 10, dtype=dtype)
-        self.assertEqual(cube.dtype, dtype)
-        self.assertEqual(cube.core_data().dtype, lazy.dtype)
-
-    def test__dtype_fill_value_clearance(self):
-        real = np.array(10.0)
-        lazy = as_lazy_data(real)
-        dtype = np.dtype('int16')
-        fill_value = 10
-        cube = Cube(lazy, dtype=dtype, fill_value=fill_value)
-        self.assertEqual(cube.dtype, dtype)
-        self.assertEqual(cube.fill_value, fill_value)
-        cube.replace(real)
-        self.assertEqual(cube.dtype, real.dtype)
-        self.assertIsNone(cube.fill_value)
-        self.assertIs(cube.core_data(), real)
-
-    def test__shape_failure(self):
-        cube = stock.simple_1d()
-        data = np.array([0])
-        emsg = 'Require data with shape \(11,\), got \(1,\).'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            cube.replace(data)
-
-    def test__lazy_failure(self):
-        cube = stock.simple_1d()
-        data = np.ones(cube.shape)
-        dtype = np.dtype('int16')
-        emsg = 'Cannot set realised dtype, no lazy data is available'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            cube.replace(data, dtype=dtype)
-
-    def test__dtype_failure(self):
-        lazy = as_lazy_data(np.array(10.0, dtype=np.dtype('float64')))
-        cube = Cube(lazy)
-        dtype = np.dtype('float32')
-        emsg = 'Can only cast lazy data to an integer or boolean dtype'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            cube.replace(lazy, dtype=dtype)
-
-    def test__promote_shape_with_dtype_failure(self):
-        data = np.array(666)
-        cube = Cube(data)
-        emsg = 'Cannot set realised dtype, no lazy data is available'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            cube.replace(data, dtype=np.dtype('float32'))
-        self.assertArrayEqual(cube.data, data)
-
-
 class Test_copy(tests.IrisTest):
     def _check_copy(self, cube, cube_copy):
         self.assertIsNot(cube_copy, cube)
@@ -1380,87 +1301,6 @@ def test__lazy(self):
         self._check_copy(cube, cube.copy())
 
 
-class Test_fill_value(tests.IrisTest):
-    def setUp(self):
-        self.dtypes = (np.dtype('int'), np.dtype('uint'),
-                       np.dtype('bool'), np.dtype('float'))
-
-    def test_cube___init___default_none(self):
-        cube = Cube(np.array(0))
-        self.assertIsNone(cube.fill_value)
-
-    def test_cube___init___setter(self):
-        fill_value = 123
-        cube = Cube(np.array(0), fill_value=fill_value)
-        self.assertEqual(cube.fill_value, fill_value)
-
-    def test_cube_setter(self):
-        fill_value = 123
-        cube = Cube(np.array(0))
-        self.assertIsNone(cube.fill_value)
-        cube.fill_value = fill_value
-        self.assertEqual(cube.fill_value, fill_value)
-
-    def test_cube_data_setter_with_ndarray(self):
-        fill_value = 123
-        cube = Cube(np.array(0), fill_value=fill_value)
-        self.assertEqual(cube.fill_value, fill_value)
-        cube.data = np.array(1)
-        self.assertIsNone(cube.fill_value)
-
-    def test_cube_data_setter_with_masked_array(self):
-        fill_value = 123
-        cube = Cube(np.array(0))
-        self.assertIsNone(cube.fill_value)
-        cube.data = ma.masked_array(1, fill_value=fill_value)
-        self.assertEqual(cube.fill_value, fill_value)
-
-    def test_fill_value_bool(self):
-        fill_value = np.bool_(True)
-        for dtype in self.dtypes:
-            data = np.array([0], dtype=dtype)
-            cube = Cube(data, fill_value=fill_value)
-            [expected] = np.array([fill_value], dtype=dtype)
-            self.assertEqual(cube.fill_value, expected)
-            self.assertEqual(cube.fill_value.dtype, dtype)
-
-    def test_fill_value_int(self):
-        fill_value = np.int_(123)
-        for dtype in self.dtypes:
-            data = np.array([0], dtype=dtype)
-            cube = Cube(data, fill_value=fill_value)
-            [expected] = np.array([fill_value], dtype=dtype)
-            self.assertEqual(cube.fill_value, expected)
-            self.assertEqual(cube.fill_value.dtype, dtype)
-
-    def test_fill_value_float(self):
-        fill_value = np.float_(123.4)
-        for dtype in self.dtypes:
-            data = np.array([0], dtype=dtype)
-            cube = Cube(data, fill_value=fill_value)
-            if dtype.kind in 'biu':
-                fill_value = np.rint(fill_value)
-            [expected] = np.array([fill_value], dtype=dtype)
-            self.assertEqual(cube.fill_value, expected)
-            self.assertEqual(cube.fill_value.dtype, dtype)
-
-    def test_fill_value_uint(self):
-        fill_value = np.uint(123)
-        for dtype in self.dtypes:
-            data = np.array([0], dtype=dtype)
-            cube = Cube(data, fill_value=fill_value)
-            [expected] = np.array([fill_value], dtype=dtype)
-            self.assertEqual(cube.fill_value, expected)
-            self.assertEqual(cube.fill_value.dtype, dtype)
-
-    def test_fill_value_overflow(self):
-        fill_value = np.float_(1e+20)
-        data = np.array([0], dtype=np.int)
-        emsg = 'Fill value of .* invalid for dtype'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            Cube(data, fill_value=fill_value)
-
-
 class Test_dtype(tests.IrisTest):
     def setUp(self):
         self.dtypes = (np.dtype('int'), np.dtype('uint'),
@@ -1472,12 +1312,6 @@ def test_real_data(self):
             cube = Cube(data)
             self.assertEqual(cube.dtype, dtype)
 
-    def test_real_data_with_dtype(self):
-        for dtype in self.dtypes:
-            data = np.array([0, 1], dtype=dtype)
-            cube = Cube(data, dtype=dtype)
-            self.assertEqual(cube.dtype, dtype)
-
     def test_real_data_masked__mask_unset(self):
         for dtype in self.dtypes:
             data = ma.array([0, 1], dtype=dtype)
@@ -1491,19 +1325,6 @@ def test_real_data_masked__mask_set(self):
             cube = Cube(data)
             self.assertEqual(cube.dtype, dtype)
 
-    def test_real_data_masked_with_dtype__mask_unset(self):
-        for dtype in self.dtypes:
-            data = ma.array([0, 1], dtype=dtype)
-            cube = Cube(data, dtype=dtype)
-            self.assertEqual(cube.dtype, dtype)
-
-    def test_real_data_masked_with_dtype__mask_set(self):
-        for dtype in self.dtypes:
-            data = ma.array([0, 1], dtype=dtype)
-            data[0] = ma.masked
-            cube = Cube(data, dtype=dtype)
-            self.assertEqual(cube.dtype, dtype)
-
     def test_lazy_data(self):
         for dtype in self.dtypes:
             data = np.array([0, 1], dtype=dtype)
@@ -1513,15 +1334,6 @@ def test_lazy_data(self):
             # of the data.
             self.assertTrue(cube.has_lazy_data())
 
-    def test_lazy_data_with_dtype(self):
-        for dtype in self.dtypes:
-            data = np.array([0, 1], dtype=dtype)
-            cube = Cube(as_lazy_data(data), dtype=dtype)
-            self.assertEqual(cube.dtype, dtype)
-            # Check that accessing the dtype does not trigger loading
-            # of the data.
-            self.assertTrue(cube.has_lazy_data())
-
     def test_lazy_data_masked__mask_unset(self):
         for dtype in self.dtypes:
             data = ma.array([0, 1], dtype=dtype)
@@ -1541,251 +1353,6 @@ def test_lazy_data_masked__mask_set(self):
             # of the data.
             self.assertTrue(cube.has_lazy_data())
 
-    def test_lazy_data_masked_with_dtype__mask_unset(self):
-        for dtype in self.dtypes:
-            data = ma.array([0, 1], dtype=dtype)
-            cube = Cube(as_lazy_data(data), dtype=dtype)
-            self.assertEqual(cube.dtype, dtype)
-            # Check that accessing the dtype does not trigger loading
-            # of the data.
-            self.assertTrue(cube.has_lazy_data())
-
-    def test_lazy_data_masked_with_dtype__mask_set(self):
-        for dtype in self.dtypes:
-            data = ma.array([0, 1], dtype=dtype)
-            data[0] = ma.masked
-            cube = Cube(as_lazy_data(data), dtype=dtype)
-            self.assertEqual(cube.dtype, dtype)
-            # Check that accessing the dtype does not trigger loading
-            # of the data.
-            self.assertTrue(cube.has_lazy_data())
-
-    def test_real_data_with_dtype_different(self):
-        for dtype in self.dtypes:
-            data = np.array([0, 1], dtype=dtype)
-            emsg = 'Cannot set realised dtype, no lazy data is available'
-            with self.assertRaisesRegexp(ValueError, emsg):
-                Cube(data, dtype=np.complex)
-
-    def test_lazy_data_masked_with_dtype__non_float_lazy_dtype(self):
-        for dtype in self.dtypes:
-            if dtype != np.dtype('float'):
-                data = ma.array([0, 1], dtype=dtype)
-                emsg = ("Cannot set realised dtype for lazy data "
-                        "with dtype\('{}'\)")
-                with self.assertRaisesRegexp(ValueError, emsg.format(dtype)):
-                    Cube(as_lazy_data(data), dtype=np.dtype('int16'))
-
-    def test_lazy_data_masked_with_dtype_non_integral(self):
-        for dtype in self.dtypes:
-            data = ma.array([0, 1], dtype=dtype)
-            data[0] = ma.masked
-            emsg = 'Can only cast lazy data to an integer or boolean dtype'
-            with self.assertRaisesRegexp(ValueError, emsg):
-                Cube(as_lazy_data(data), dtype=np.complex)
-
-
-class Test_data_dtype_fillvalue(tests.IrisTest):
-    def _sample_data(self, dtype='f4', masked=False, lazy=False):
-        data = np.arange(6).reshape((2, 3))
-        dtype = np.dtype(dtype)
-        data = data.astype(dtype)
-        if masked:
-            data = ma.masked_array(data, mask=[[0, 1, 0], [0, 0, 0]])
-        if lazy:
-            data = as_lazy_data(data)
-        return data
-
-    def _sample_cube(self, dtype='f4', masked=False, lazy=False,
-                     cube_dtype=None, cube_fill_value=None):
-        data = self._sample_data(dtype=dtype, masked=masked, lazy=lazy)
-        if cube_dtype is None:
-            cube_dtype = dtype
-            # NOTE: with masked lazy integers, the resulting data dtype will
-            # be changed, so we must set the cube to the 'original' dtype.
-        else:
-            cube_dtype = np.dtype(cube_dtype)
-        cube = Cube(data, dtype=cube_dtype, fill_value=cube_fill_value)
-        return cube
-
-    def test_realdata_change(self):
-        # Check that re-assigning real data resets dtype and fill_value.
-        cube = self._sample_cube(cube_fill_value=27.3)
-        self.assertEqual(cube.dtype, np.dtype('f4'))
-        self.assertArrayAllClose(cube.fill_value, 27.3)
-        new_data = self._sample_data(dtype=np.int32)
-        cube.data = new_data
-        self.assertIs(cube.core_data(), new_data)
-        self.assertEqual(cube.dtype, np.dtype('i4'))
-        self.assertIsNone(cube.fill_value)
-
-    def test_realise_unmasked(self):
-        # Check that touching unmasked lazy data retains the fill_value.
-        cube = self._sample_cube(cube_fill_value=27.3, lazy=True)
-        data = cube.data
-        self.assertIs(cube.core_data(), data)
-        self.assertArrayAllClose(cube.fill_value, 27.3)
-
-    def test_realise_masked(self):
-        # Check that touching masked lazy data retains the fill_value.
-        fill_value = 27.3
-        cube = self._sample_cube(cube_fill_value=fill_value, masked=True,
-                                 lazy=True)
-        data = cube.data
-        self.assertIs(cube.core_data(), data)
-        self.assertArrayAllClose(cube.fill_value, fill_value)
-        self.assertArrayAllClose(data.fill_value, fill_value)
-
-    def test_realise_maskedints(self):
-        # Check that touching masked integer lazy data retains the fill_value.
-        fill_value = 999
-        cube = self._sample_cube(dtype=np.int16, masked=True, lazy=True,
-                                 cube_fill_value=fill_value)
-        self.assertIs(cube.core_data().dtype, np.dtype('f8'))
-        data = cube.data
-        self.assertIs(cube.core_data().dtype, np.dtype('i2'))
-        self.assertEqual(cube.fill_value.dtype, np.dtype('i2'))
-        self.assertArrayAllClose(cube.fill_value, fill_value)
-        self.assertArrayAllClose(data.fill_value, fill_value)
-
-    def test_lazydata_change(self):
-        # Check that re-assigning lazy data resets dtype and fill_value.
-        cube = self._sample_cube(dtype=np.float32, lazy=True,
-                                 cube_dtype=np.int16,
-                                 cube_fill_value=27.3)
-        # Set a modified dtype to check it gets reset.
-        self.assertEqual(cube.dtype, np.dtype('i2'))
-        self.assertEqual(cube.core_data().dtype, np.dtype('f4'))
-        self.assertArrayAllClose(cube.fill_value, 27)
-        new_data = self._sample_data(np.float64, lazy=True)
-        cube.data = new_data
-        self.assertEqual(cube.dtype, np.dtype('f8'))
-        self.assertIsNone(cube.fill_value)
-
-    def test_lazydata_nonmaskedints(self):
-        # Check that lazy ints retain their dtype.
-        data_original = self._sample_data(dtype=np.int32)
-        data_lazy = as_lazy_data(data_original)
-        cube = Cube(data_lazy)
-        self.assertEqual(cube.dtype, np.dtype('i4'))
-        self.assertEqual(cube.core_data().dtype, np.dtype('i4'))
-        data = cube.data
-        self.assertArrayEqual(data, data_original)
-
-    def test_lazydata_maskedints(self):
-        # Check lazy masked ints dtype.
-        fill_value = 1234
-        masked_data_original = self._sample_data(dtype=np.int32, masked=True)
-        masked_data_lazy = as_lazy_data(masked_data_original)
-        cube = Cube(masked_data_lazy, dtype=masked_data_original.dtype,
-                    fill_value=fill_value)
-        self.assertEqual(cube.dtype, np.dtype('i4'))
-        self.assertEqual(cube.core_data().dtype, np.dtype('f8'))
-        data = cube.data
-        self.assertTrue(ma.is_masked(data))
-        self.assertMaskedArrayEqual(data, masked_data_original)
-        self.assertArrayAllClose(cube.fill_value, fill_value)
-        self.assertArrayAllClose(data.fill_value, fill_value)
-
-    def test_realdata_maskedconstantint(self):
-        fill_value = 1234
-        masked_data = ma.masked_array([666], mask=True)
-        masked_constant = masked_data[0]
-        cube = Cube(masked_constant, fill_value=fill_value)
-        self.assertArrayAllClose(cube.fill_value, fill_value)
-        data = cube.data
-        self.assertTrue(ma.isMaskedArray(data))
-        self.assertArrayAllClose(cube.fill_value, fill_value)
-        self.assertArrayAllClose(data.fill_value, fill_value)
-        self.assertNotIsInstance(data, ma.core.MaskedConstant)
-
-    def test_lazydata_maskedconstantint(self):
-        fill_value = 1234
-        dtype = np.dtype('i2')
-        masked_data = ma.masked_array([666], mask=True, dtype=dtype)
-        masked_constant = masked_data[0]
-        masked_constant_lazy = as_lazy_data(masked_constant)
-        cube = Cube(masked_constant_lazy, dtype=dtype, fill_value=fill_value)
-        self.assertArrayAllClose(cube.fill_value, fill_value)
-        self.assertEqual(cube.dtype, dtype)
-        self.assertEqual(cube.core_data().dtype, np.dtype('f8'))
-        data = cube.data
-        self.assertTrue(ma.isMaskedArray(data))
-        self.assertArrayAllClose(cube.fill_value, fill_value)
-        self.assertArrayAllClose(data.fill_value, fill_value)
-        self.assertEqual(data.dtype, dtype)
-        self.assertNotIsInstance(data, ma.core.MaskedConstant)
-
-    def test_fill_value__int_dtype_to_float(self):
-        # Check that fill_value is cast to dtype, e.g. float --> int.
-        cube = self._sample_cube(dtype=np.float32, cube_fill_value=1735)
-        self.assertEqual(cube.fill_value.dtype, np.dtype('f4'))
-        self.assertArrayAllClose(cube.fill_value, 1735.0)
-
-    def test_fill_value__float_dtype_to_int(self):
-        # Check that fill_value is rounded to dtype, e.g. float --> int.
-        cube = self._sample_cube(dtype=np.int16, cube_fill_value=1734.99999)
-        self.assertEqual(cube.fill_value.dtype, np.dtype('i2'))
-        self.assertArrayAllClose(cube.fill_value, 1735)
-
-    def test_set_fill_value(self):
-        cube = self._sample_cube()
-        cube.fill_value = -74.6
-        self.assertEqual(cube.fill_value.dtype, np.dtype('f4'))
-        self.assertArrayAllClose(cube.fill_value, -74.6)
-
-    def test_set_fill_value__typecast(self):
-        cube = self._sample_cube(dtype=np.int16)
-        cube.fill_value = -74.6
-        self.assertEqual(cube.fill_value.dtype, np.dtype('i2'))
-        self.assertArrayAllClose(cube.fill_value, -75)
-
-    def test_set_fill_value__casterror(self):
-        cube = self._sample_cube(dtype=np.int16)
-        msg = "Fill value of .* invalid for dtype\('int16'\)"
-        with self.assertRaisesRegexp(ValueError, msg):
-            # NOTE: this doesn't actually work properly in most cases.
-            # E.G. it will happily assign 1e12 to an int16 and gets 4096.
-            cube.fill_value = -1.0e23
-
-    def test_clear_fill_value(self):
-        cube = self._sample_cube(cube_fill_value=123.768)
-        cube.fill_value = None
-        self.assertIsNone(cube.fill_value)
-
-    def test_realdata___getitem__(self):
-        fill_value = 123
-        cube = Cube(np.arange(10), fill_value=fill_value)
-        subcube = cube[5:]
-        self.assertArrayAllClose(subcube.fill_value, fill_value)
-
-    def test_lazydata___getitem__(self):
-        fill_value = 123
-        dtype = np.dtype('int16')
-        masked_array = ma.masked_array(np.arange(5),
-                                       mask=[0, 0, 1, 0, 0],
-                                       dtype=dtype)
-        lazy_masked_array = as_lazy_data(masked_array)
-        cube = Cube(lazy_masked_array, dtype=dtype, fill_value=fill_value)
-        subcube = cube[3:]
-        self.assertEqual(subcube.dtype, dtype)
-        self.assertArrayAllClose(subcube.fill_value, fill_value)
-
-    def test_data_getter__masked_with_fill_value(self):
-        fill_value = 1234
-        cube = self._sample_cube(masked=True,
-                                 cube_fill_value=fill_value)
-        self.assertEqual(cube.fill_value, fill_value)
-        data = cube.data
-        self.assertEqual(data.fill_value, fill_value)
-
-    def test_data_getter__masked_with_fill_value_default(self):
-        cube = self._sample_cube(masked=True)
-        self.assertIsNone(cube.fill_value)
-        data = cube.data
-        np_fill_value = ma.masked_array(0, dtype=cube.dtype).fill_value
-        self.assertEqual(data.fill_value, np_fill_value)
-
 
 class TestSubset(tests.IrisTest):
     def test_scalar_coordinate(self):
diff --git a/lib/iris/tests/unit/data_manager/test_DataManager.py b/lib/iris/tests/unit/data_manager/test_DataManager.py
index 61eae3b357..4d9fe2cce3 100644
--- a/lib/iris/tests/unit/data_manager/test_DataManager.py
+++ b/lib/iris/tests/unit/data_manager/test_DataManager.py
@@ -79,17 +79,6 @@ def test_real_with_real_failure(self):
         dm2 = DataManager(np.ones(self.shape))
         self.assertFalse(dm1 == dm2)
 
-    def test_real_with_real__fill_value(self):
-        fill_value = 1234
-        dm1 = DataManager(self.real_array, fill_value=fill_value)
-        dm2 = DataManager(self.real_array, fill_value=fill_value)
-        self.assertEqual(dm1, dm2)
-
-    def test_real_with_real__fill_value_failure(self):
-        dm1 = DataManager(self.real_array, fill_value=1234)
-        dm2 = DataManager(self.real_array, fill_value=4321)
-        self.assertFalse(dm1 == dm2)
-
     def test_real_with_real__dtype_failure(self):
         dm1 = DataManager(self.real_array)
         dm2 = DataManager(self.real_array.astype(int))
@@ -111,41 +100,11 @@ def test_lazy_with_lazy_failure(self):
         dm2 = DataManager(as_lazy_data(self.real_array) * 10)
         self.assertFalse(dm1 == dm2)
 
-    def test_lazy_with_lazy__fill_value(self):
-        fill_value = 1234
-        dm1 = DataManager(as_lazy_data(self.real_array),
-                          fill_value=fill_value)
-        dm2 = DataManager(as_lazy_data(self.real_array),
-                          fill_value=fill_value)
-        self.assertEqual(dm1, dm2)
-
-    def test_lazy_with_lazy__fill_value_failure(self):
-        dm1 = DataManager(as_lazy_data(self.real_array),
-                          fill_value=1234)
-        dm2 = DataManager(as_lazy_data(self.real_array),
-                          fill_value=4321)
-        self.assertFalse(dm1 == dm2)
-
     def test_lazy_with_lazy__dtype_failure(self):
         dm1 = DataManager(as_lazy_data(self.real_array))
         dm2 = DataManager(as_lazy_data(self.real_array).astype(int))
         self.assertFalse(dm1 == dm2)
 
-    def test_lazy_with_lazy__realised_dtype(self):
-        dtype = np.dtype('int16')
-        dm1 = DataManager(as_lazy_data(self.real_array),
-                          realised_dtype=dtype)
-        dm2 = DataManager(as_lazy_data(self.real_array),
-                          realised_dtype=dtype)
-        self.assertEqual(dm1, dm2)
-
-    def test_lazy_with_lazy__realised_dtype_failure(self):
-        dm1 = DataManager(as_lazy_data(self.real_array),
-                          realised_dtype=np.dtype('int8'))
-        dm2 = DataManager(as_lazy_data(self.real_array),
-                          realised_dtype=np.dtype('int16'))
-        self.assertFalse(dm1 == dm2)
-
     def test_non_DataManager_failure(self):
         dm = DataManager(np.array(0))
         self.assertFalse(dm == 0)
@@ -167,17 +126,6 @@ def test_real_with_real_failure(self):
         dm2 = DataManager(self.real_array.copy())
         self.assertFalse(dm1 != dm2)
 
-    def test_real_with_real__fill_value(self):
-        dm1 = DataManager(self.real_array, fill_value=1234)
-        dm2 = DataManager(self.real_array, fill_value=4321)
-        self.assertNotEqual(dm1, dm2)
-
-    def test_real_with_real__fill_value_failure(self):
-        fill_value = 1234
-        dm1 = DataManager(self.real_array, fill_value=fill_value)
-        dm2 = DataManager(self.real_array, fill_value=fill_value)
-        self.assertFalse(dm1 != dm2)
-
     def test_real_with_real__dtype(self):
         dm1 = DataManager(self.real_array)
         dm2 = DataManager(self.real_array.astype(int))
@@ -199,41 +147,11 @@ def test_lazy_with_lazy_failure(self):
         dm2 = DataManager(as_lazy_data(self.real_array))
         self.assertFalse(dm1 != dm2)
 
-    def test_lazy_with_lazy__fill_value(self):
-        dm1 = DataManager(as_lazy_data(self.real_array),
-                          fill_value=1234)
-        dm2 = DataManager(as_lazy_data(self.real_array),
-                          fill_value=4321)
-        self.assertNotEqual(dm1, dm2)
-
-    def test_lazy_with_lazy__fill_value_failure(self):
-        fill_value = 1234
-        dm1 = DataManager(as_lazy_data(self.real_array),
-                          fill_value=fill_value)
-        dm2 = DataManager(as_lazy_data(self.real_array),
-                          fill_value=fill_value)
-        self.assertFalse(dm1 != dm2)
-
     def test_lazy_with_lazy__dtype(self):
         dm1 = DataManager(as_lazy_data(self.real_array))
         dm2 = DataManager(as_lazy_data(self.real_array).astype(int))
         self.assertNotEqual(dm1, dm2)
 
-    def test_lazy_with_lazy__realised_dtype(self):
-        dm1 = DataManager(as_lazy_data(self.real_array),
-                          realised_dtype=np.dtype('int8'))
-        dm2 = DataManager(as_lazy_data(self.real_array),
-                          realised_dtype=np.dtype('int16'))
-        self.assertNotEqual(dm1, dm2)
-
-    def test_lazy_with_lazy__realised_dtype_failure(self):
-        dtype = np.dtype('int16')
-        dm1 = DataManager(as_lazy_data(self.real_array),
-                          realised_dtype=dtype)
-        dm2 = DataManager(as_lazy_data(self.real_array),
-                          realised_dtype=dtype)
-        self.assertFalse(dm1 != dm2)
-
     def test_non_DataManager(self):
         dm = DataManager(np.array(0))
         self.assertNotEqual(dm, 0)
@@ -252,46 +170,12 @@ def test_real(self):
         expected = '{}({!r})'.format(self.name, self.real_array)
         self.assertEqual(result, expected)
 
-    def test_real__fill_value(self):
-        fill_value = 1234
-        dm = DataManager(self.real_array, fill_value=fill_value)
-        result = repr(dm)
-        fmt = '{}({!r}, fill_value={!r})'
-        expected = fmt.format(self.name, self.real_array, fill_value)
-        self.assertEqual(result, expected)
-
     def test_lazy(self):
         dm = DataManager(self.lazy_array)
         result = repr(dm)
         expected = '{}({!r})'.format(self.name, self.lazy_array)
         self.assertEqual(result, expected)
 
-    def test_lazy__fill_value(self):
-        fill_value = 1234.0
-        dm = DataManager(self.lazy_array, fill_value=fill_value)
-        result = repr(dm)
-        fmt = '{}({!r}, fill_value={!r})'
-        expected = fmt.format(self.name, self.lazy_array, fill_value)
-        self.assertEqual(result, expected)
-
-    def test_lazy__realised_dtype(self):
-        dtype = np.dtype('int16')
-        dm = DataManager(self.lazy_array, realised_dtype=dtype)
-        result = repr(dm)
-        fmt = '{}({!r}, realised_dtype={!r})'
-        expected = fmt.format(self.name, self.lazy_array, dtype)
-        self.assertEqual(result, expected)
-
-    def test_lazy__fill_value_realised_dtype(self):
-        fill_value = 1234
-        dtype = np.dtype('int16')
-        dm = DataManager(self.lazy_array, fill_value=fill_value,
-                         realised_dtype=dtype)
-        result = repr(dm)
-        fmt = '{}({!r}, fill_value={!r}, realised_dtype={!r})'
-        expected = fmt.format(self.name, self.lazy_array, fill_value, dtype)
-        self.assertEqual(result, expected)
-
 
 class Test__assert_axioms(tests.IrisTest):
     def setUp(self):
@@ -311,29 +195,6 @@ def test_array_all(self):
         with self.assertRaisesRegexp(AssertionError, emsg):
             self.dm._assert_axioms()
 
-    def test_realised_dtype(self):
-        self.dm._realised_dtype = np.dtype('float')
-        emsg = 'Unexpected realised dtype state, got dtype'
-        with self.assertRaisesRegexp(AssertionError, emsg):
-            self.dm._assert_axioms()
-
-    def test_real_array_with_realised_dtype(self):
-        self.dm._realised_dtype = np.dtype('int')
-        emsg = ("Unexpected real data with realised dtype, got "
-                "real data and realised dtype\('int64'\)")
-        with self.assertRaisesRegexp(AssertionError, emsg):
-            self.dm._assert_axioms()
-
-    def test_non_float_lazy_array_with_realised_dtype(self):
-        self.dm._real_array = None
-        self.dm._lazy_array = self.lazy_array
-        self.dm._realised_dtype = np.dtype('int')
-        emsg = ("Unexpected lazy data dtype with realised dtype, got "
-                "lazy data dtype\('int64'\) and realised "
-                "dtype\('int64'\)")
-        with self.assertRaisesRegexp(AssertionError, emsg):
-            self.dm._assert_axioms()
-
 
 class Test__deepcopy(tests.IrisTest):
     def setUp(self):
@@ -384,34 +245,6 @@ def test_lazy_with_lazy(self):
         self.assertEqual(result, expected)
         self.assertIs(result._lazy_array, data)
 
-    def test_real_with_realised_dtype_failure(self):
-        dm = DataManager(self.real_array)
-        emsg = 'Cannot copy'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            dm._deepcopy(self.memo, realised_dtype=np.dtype('int16'))
-
-    def test_lazy_with_realised_dtype__lazy_dtype_failure(self):
-        dm = DataManager(as_lazy_data(self.real_array).astype(int))
-        emsg = 'Cannot copy'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            dm._deepcopy(self.memo, realised_dtype=np.dtype('int16'))
-
-    def test_lazy_with_realised_dtype_failure(self):
-        dm = DataManager(as_lazy_data(self.real_array))
-        emsg = 'Cannot copy'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            dm._deepcopy(self.memo, realised_dtype=np.dtype('float32'))
-
-    def test_lazy_with_realised_dtype(self):
-        dm = DataManager(as_lazy_data(self.real_array),
-                         realised_dtype=np.dtype('int16'))
-        data = as_lazy_data(self.real_array) * 10
-        dtype = np.dtype('int8')
-        result = dm._deepcopy(self.memo, data=data, realised_dtype=dtype)
-        expected = DataManager(data, realised_dtype=dtype)
-        self.assertEqual(result, expected)
-        self.assertIs(result._lazy_array, data)
-
     def test_real_with_real_failure(self):
         dm = DataManager(self.real_array)
         emsg = 'Cannot copy'
@@ -436,140 +269,6 @@ def test_lazy_with_lazy_failure(self):
         with self.assertRaisesRegexp(ValueError, emsg):
             dm._deepcopy(self.memo, data=as_lazy_data(np.array(0)))
 
-    def test__default_fill_value(self):
-        dm = DataManager(np.array(0))
-        self.assertIsNone(dm.fill_value)
-        result = dm._deepcopy(self.memo)
-        self.assertIsNone(result.fill_value)
-
-    def test__default_with_fill_value(self):
-        fill_value = 1234
-        dm = DataManager(np.array(0), fill_value=fill_value)
-        self.assertEqual(dm.fill_value, fill_value)
-        result = dm._deepcopy(self.memo)
-        self.assertEqual(result.fill_value, fill_value)
-
-    def test__clear_fill_value(self):
-        fill_value = 1234
-        dm = DataManager(np.array(0), fill_value=fill_value)
-        self.assertEqual(dm.fill_value, fill_value)
-        result = dm._deepcopy(self.memo, fill_value=None)
-        self.assertIsNone(result.fill_value)
-
-    def test__set_fill_value(self):
-        fill_value = 1234
-        dm = DataManager(np.array(0))
-        self.assertIsNone(dm.fill_value)
-        result = dm._deepcopy(self.memo, fill_value=fill_value)
-        self.assertEqual(result.fill_value, fill_value)
-
-    def test__set_fill_value_failure(self):
-        dm = DataManager(np.array(0))
-        self.assertIsNone(dm.fill_value)
-        emsg = 'Cannot copy'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            dm._deepcopy(self.memo, fill_value=1e+20)
-
-
-class Test__propagate_masked_data_fill_value(tests.IrisTest):
-    def setUp(self):
-        self.real_array = np.array(0)
-        self.mask_array = ma.array(0)
-        np_fill_value = ma.array(0, dtype=self.mask_array.dtype).fill_value
-        assert np_fill_value == self.mask_array.fill_value
-        self.np_fill_value = np_fill_value
-        self.dm = DataManager(self.mask_array)
-        self.dm.fill_value = None
-
-    def test_nop__with_real_array(self):
-        fill_value = 1234
-        dm = DataManager(self.real_array)
-        dm.fill_value = 1234
-        self.assertEqual(dm.fill_value, fill_value)
-        dm._propagate_masked_data_fill_value()
-        self.assertEqual(dm.fill_value, fill_value)
-
-    def test_clear_fill_value__with_np_default(self):
-        fill_value = 1234
-        self.dm.fill_value = fill_value
-        self.assertEqual(self.dm.fill_value, fill_value)
-        self.dm._propagate_masked_data_fill_value()
-        self.assertIsNone(self.dm.fill_value)
-
-    def test_set_fill_value(self):
-        fill_value = 1234
-        self.assertIsNone(self.dm.fill_value)
-        self.dm._real_array.fill_value = fill_value
-        self.dm._propagate_masked_data_fill_value()
-        self.assertEqual(self.dm.fill_value, fill_value)
-
-
-class Test__realised_dtype_setter(tests.IrisTest):
-    def setUp(self):
-        self.real_array = np.array(0.0)
-        self.lazy_array = as_lazy_data(self.real_array)
-        self.dm = DataManager(self.lazy_array)
-
-    def test_lazy_with_none(self):
-        self.assertIsNone(self.dm._realised_dtype)
-        self.dm._realised_dtype_setter(None)
-        self.assertIsNone(self.dm._realised_dtype)
-
-    def test_real_with_none(self):
-        self.dm._lazy_array = None
-        self.dm._real_array = self.real_array
-        self.assertIsNone(self.dm._realised_dtype)
-        self.dm._realised_dtype_setter(None)
-        self.assertIsNone(self.dm._realised_dtype)
-
-    def test_real_with_same_dtype(self):
-        self.dm._lazy_array = None
-        self.dm._real_array = self.real_array
-        self.assertIsNone(self.dm._realised_dtype)
-        self.dm._realised_dtype_setter(self.dm.dtype)
-        self.assertIsNone(self.dm._realised_dtype)
-
-    def test_lazy_with_same_dtype(self):
-        self.assertIsNone(self.dm._realised_dtype)
-        self.dm._realised_dtype_setter(self.dm.dtype)
-        self.assertIsNone(self.dm._realised_dtype)
-
-    def test_real_array_failure(self):
-        self.dm._lazy_array = None
-        self.dm._real_array = self.real_array
-        self.assertIsNone(self.dm._realised_dtype)
-        emsg = 'Cannot set realised dtype, no lazy data is available'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            self.dm._realised_dtype_setter(np.dtype('int16'))
-
-    def test_invalid_realised_dtype(self):
-        emsg = ("Can only cast lazy data to an integer or boolean "
-                "dtype, got dtype\('float32'\)")
-        with self.assertRaisesRegexp(ValueError, emsg):
-            self.dm._realised_dtype_setter(np.dtype('float32'))
-
-    def test_lazy_with_realised_dtype(self):
-        dtypes = (np.dtype('bool'), np.dtype('int16'), np.dtype('uint16'))
-        for dtype in dtypes:
-            self.dm._realised_dtype = None
-            self.dm._realised_dtype_setter(dtype)
-            self.assertEqual(self.dm._realised_dtype, dtype)
-
-    def test_lazy_with_realised_dtype__lazy_dtype_failure(self):
-        self.dm._lazy_array = self.lazy_array.astype(np.dtype('int64'))
-        emsg = ("Cannot set realised dtype for lazy data "
-                "with dtype\('int64'\)")
-        with self.assertRaisesRegexp(ValueError, emsg):
-            self.dm._realised_dtype_setter(np.dtype('int16'))
-
-    def test_lazy_replace_with_none(self):
-        self.assertIsNone(self.dm._realised_dtype)
-        dtype = np.dtype('int16')
-        self.dm._realised_dtype_setter(dtype)
-        self.assertEqual(self.dm._realised_dtype, dtype)
-        self.dm._realised_dtype_setter(None)
-        self.assertIsNone(self.dm._realised_dtype)
-
 
 class Test_data__getter(tests.IrisTest):
     def setUp(self):
@@ -598,72 +297,6 @@ def test_with_lazy_array(self):
         self.assertFalse(dm.has_lazy_data())
         self.assertArrayEqual(result, self.real_array)
 
-    def test_with_real_mask_array__default_fill_value(self):
-        fill_value = 1234
-        self.mask_array.fill_value = fill_value
-        dm = DataManager(self.mask_array)
-        self.assertEqual(dm.fill_value, fill_value)
-        self.assertEqual(dm.data.fill_value, fill_value)
-
-    def test_with_real_mask_array__with_fill_value_None(self):
-        fill_value = 1234
-        self.mask_array.fill_value = fill_value
-        dm = DataManager(self.mask_array, fill_value=None)
-        self.assertIsNone(dm.fill_value)
-        np_fill_value = ma.array(0, dtype=dm.dtype).fill_value
-        self.assertEqual(dm.data.fill_value, np_fill_value)
-
-    def test_with_real_mask_array__with_fill_value(self):
-        fill_value = 1234
-        dm = DataManager(self.mask_array, fill_value=fill_value)
-        self.assertEqual(dm.fill_value, fill_value)
-        self.assertEqual(dm.data.fill_value, fill_value)
-
-    def test_with_lazy_mask_array__masked_default_fill_value(self):
-        dm = DataManager(self.lazy_mask_array_masked,
-                         realised_dtype=self.realised_dtype)
-        self.assertIsNone(dm.fill_value)
-        np_fill_value = ma.array(0, dtype=dm.dtype).fill_value
-        self.assertEqual(dm.data.fill_value, np_fill_value)
-
-    def test_with_lazy_mask_array__masked_fill_value_None(self):
-        dm = DataManager(self.lazy_mask_array_masked,
-                         fill_value=None,
-                         realised_dtype=self.realised_dtype)
-        self.assertIsNone(dm.fill_value)
-        np_fill_value = ma.array(0, dtype=dm.dtype).fill_value
-        self.assertEqual(dm.data.fill_value, np_fill_value)
-
-    def test_with_lazy_mask_array__masked_with_fill_value(self):
-        fill_value = 1234
-        dm = DataManager(self.lazy_mask_array_masked,
-                         fill_value=fill_value,
-                         realised_dtype=self.realised_dtype)
-        self.assertEqual(dm.fill_value, fill_value)
-        self.assertEqual(dm.data.fill_value, fill_value)
-
-    def test_with_lazy_mask_array__not_masked(self):
-        dm = DataManager(self.lazy_mask_array,
-                         realised_dtype=self.realised_dtype)
-        self.assertTrue(dm.has_lazy_data())
-        result = dm.data
-        self.assertFalse(dm.has_lazy_data())
-        self.assertIsInstance(result, np.core.ndarray)
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, self.realised_dtype)
-        self.assertArrayEqual(result, self.real_array)
-
-    def test_with_lazy_mask_array__masked(self):
-        dm = DataManager(self.lazy_mask_array_masked,
-                         realised_dtype=self.realised_dtype)
-        self.assertTrue(dm.has_lazy_data())
-        result = dm.data
-        self.assertFalse(dm.has_lazy_data())
-        self.assertIsInstance(result, ma.MaskedArray)
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, self.realised_dtype)
-        self.assertArrayEqual(result, self.mask_array_masked)
-
     def test_with_real_masked_constant(self):
         masked_data = ma.masked_array([666], mask=True, dtype=np.dtype('f8'))
         masked_constant = masked_data[0]
@@ -674,19 +307,6 @@ def test_with_real_masked_constant(self):
         self.assertNotIsInstance(result, ma.core.MaskedConstant)
         self.assertMaskedArrayEqual(result, masked_data)
 
-    def test_with_lazy_masked_constant(self):
-        dtype = np.dtype('int16')
-        masked_data = ma.masked_array([666], mask=True, dtype=dtype)
-        masked_constant = masked_data[0]
-        lazy_masked_constant = as_lazy_data(masked_constant)
-        dm = DataManager(lazy_masked_constant, realised_dtype=dtype)
-        self.assertEqual(dm.dtype, dtype)
-        result = dm.data
-        self.assertFalse(dm.has_lazy_data())
-        self.assertIsInstance(result, ma.MaskedArray)
-        self.assertNotIsInstance(result, ma.core.MaskedConstant)
-        self.assertMaskedArrayEqual(result, masked_data)
-
 
 class Test_data__setter(tests.IrisTest):
     def test_zero_ndim_real_with_scalar_int(self):
@@ -818,35 +438,6 @@ def test_nd_lazy_to_nd_lazy(self):
         self.assertTrue(dm.has_lazy_data())
         self.assertArrayEqual(dm.data, lazy_array.compute())
 
-    def test_realised_dtype_none(self):
-        shape = (2, 3, 4)
-        size = np.prod(shape)
-        mask_array = ma.arange(size).reshape(shape)
-        dtype = mask_array.dtype
-        lazy_array = as_lazy_data(mask_array)
-        dm = DataManager(lazy_array, realised_dtype=dtype)
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, dtype)
-        dm.data = mask_array
-        self.assertIs(dm.data, mask_array)
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, dtype)
-
-    def test_realised_dtype_clearance(self):
-        shape = (2, 3, 4)
-        size = np.prod(shape)
-        mask_array = ma.arange(size).reshape(shape)
-        mask_array[0, 0, 0] = ma.masked
-        dtype = mask_array.dtype
-        lazy_array = as_lazy_data(mask_array)
-        dm = DataManager(lazy_array, realised_dtype=dtype)
-        self.assertEqual(dm._realised_dtype, dtype)
-        self.assertEqual(dm.dtype, dtype)
-        dm.data = mask_array
-        self.assertIs(dm.data, mask_array)
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, dtype)
-
     def test_coerce_to_ndarray(self):
         shape = (2, 3)
         size = np.prod(shape)
@@ -868,36 +459,6 @@ def test_real_masked_constant_to_array(self):
         self.assertNotIsInstance(dm.data, ma.core.MaskedConstant)
         self.assertMaskedArrayEqual(dm.data, masked_data)
 
-    def test_real_array__fill_value_clearance(self):
-        fill_value = 1234
-        dm = DataManager(np.array(0), fill_value=fill_value)
-        self.assertEqual(dm.fill_value, fill_value)
-        dm.data = np.array(1)
-        self.assertIsNone(dm.fill_value)
-
-    def test_lazy_array__fill_value_clearance(self):
-        fill_value = 1234
-        dm = DataManager(as_lazy_data(np.array(0)),
-                         fill_value=fill_value)
-        self.assertEqual(dm.fill_value, fill_value)
-        dm.data = as_lazy_data(np.array(1))
-        self.assertIsNone(dm.fill_value)
-
-    def test_mask_array__default_fill_value(self):
-        dm = DataManager(np.array(0))
-        self.assertIsNone(dm.fill_value)
-        data = ma.array(1)
-        dm.data = data
-        self.assertIsNone(dm.fill_value)
-
-    def test_mask_array__with_fill_value(self):
-        dm = DataManager(np.array(0))
-        self.assertIsNone(dm.fill_value)
-        fill_value = 1234
-        data = ma.array(1, fill_value=fill_value)
-        dm.data = data
-        self.assertEqual(dm.fill_value, fill_value)
-
 
 class Test_dtype(tests.IrisTest):
     def setUp(self):
@@ -912,76 +473,6 @@ def test_lazy_array(self):
         dm = DataManager(self.lazy_array)
         self.assertEqual(dm.dtype, np.dtype('float64'))
 
-    def test_lazy_array_realised_dtype(self):
-        dm = DataManager(self.lazy_array, realised_dtype=np.dtype('bool'))
-        self.assertEqual(dm.dtype, np.dtype('bool'))
-        self.assertEqual(dm._lazy_array.dtype, np.dtype('float64'))
-
-
-class Test_fill_value(tests.IrisTest):
-    def setUp(self):
-        self.dtypes = (np.dtype('int'), np.dtype('uint'),
-                       np.dtype('bool'), np.dtype('float'))
-
-    def test___init___default(self):
-        dm = DataManager(np.array(0))
-        self.assertIsNone(dm.fill_value)
-
-    def test___init___with_fill_value(self):
-        fill_value = 1234
-        dm = DataManager(np.array(0), fill_value=fill_value)
-        self.assertEqual(dm.fill_value, fill_value)
-
-    def test_fill_value_bool(self):
-        fill_value = np.bool_(True)
-        for dtype in self.dtypes:
-            data = np.array([0], dtype=dtype)
-            dm = DataManager(data)
-            dm.fill_value = fill_value
-            [expected] = np.asarray([fill_value], dtype=dtype)
-            self.assertEqual(dm.fill_value, expected)
-            self.assertEqual(dm.fill_value.dtype, dtype)
-
-    def test_fill_value_int(self):
-        fill_value = np.int(1234)
-        for dtype in self.dtypes:
-            data = np.array([0], dtype=dtype)
-            dm = DataManager(data)
-            dm.fill_value = fill_value
-            [expected] = np.asarray([fill_value], dtype=dtype)
-            self.assertEqual(dm.fill_value, expected)
-            self.assertEqual(dm.fill_value.dtype, dtype)
-
-    def test_fill_value_float(self):
-        fill_value = np.float(123.4)
-        for dtype in self.dtypes:
-            data = np.array([0], dtype=dtype)
-            dm = DataManager(data)
-            dm.fill_value = fill_value
-            if dtype.kind in 'biu':
-                fill_value = np.rint(fill_value)
-            [expected] = np.asarray([fill_value], dtype=dtype)
-            self.assertEqual(dm.fill_value, expected)
-            self.assertEqual(dm.fill_value.dtype, dtype)
-
-    def test_fill_value_uint(self):
-        fill_value = np.uint(1234)
-        for dtype in self.dtypes:
-            data = np.array([0], dtype=dtype)
-            dm = DataManager(data)
-            dm.fill_value = fill_value
-            [expected] = np.array([fill_value], dtype=dtype)
-            self.assertEqual(dm.fill_value, expected)
-            self.assertEqual(dm.fill_value.dtype, dtype)
-
-    def test_fill_value_overflow(self):
-        fill_value = np.float(1e+20)
-        data = np.array([0], dtype=np.int32)
-        dm = DataManager(data)
-        emsg = 'Fill value of .* invalid for dtype'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            dm.fill_value = fill_value
-
 
 class Test_ndim(tests.IrisTest):
     def test_ndim_0(self):
@@ -1030,35 +521,13 @@ def setUp(self):
 
     def test(self):
         dm = DataManager(np.array(0))
-        kwargs = dict(data=self.data, fill_value='none', realised_dtype='none')
+        kwargs = dict(data=self.data)
         with mock.patch(self.method) as mocker:
             mocker.return_value = self.return_value
             result = dm.copy(data=self.data)
             mocker.assert_called_once_with(self.memo, **kwargs)
         self.assertIs(result, self.return_value)
 
-    def test_with_fill_value(self):
-        dm = DataManager(np.array(0))
-        fill_value = mock.sentinel.fill_value
-        kwargs = dict(data=self.data, fill_value=fill_value,
-                      realised_dtype='none')
-        with mock.patch(self.method) as mocker:
-            mocker.return_value = self.return_value
-            result = dm.copy(data=self.data, fill_value=fill_value)
-            mocker.assert_called_once_with(self.memo, **kwargs)
-        self.assertIs(result, self.return_value)
-
-    def test_with_realised_dtype(self):
-        dm = DataManager(np.array(0))
-        realised_dtype = mock.sentinel.realised_dtype
-        kwargs = dict(data=self.data, fill_value='none',
-                      realised_dtype=realised_dtype)
-        with mock.patch(self.method) as mocker:
-            mocker.return_value = self.return_value
-            result = dm.copy(data=self.data, realised_dtype=realised_dtype)
-            mocker.assert_called_once_with(self.memo, **kwargs)
-        self.assertIs(result, self.return_value)
-
 
 class Test_core_data(tests.IrisTest):
     def test_real_array(self):
@@ -1107,157 +576,5 @@ def test_with_lazy_array(self):
         self.assertIs(result, dm._lazy_array)
 
 
-class Test_replace(tests.IrisTest):
-    def setUp(self):
-        self.shape = (2, 3, 4)
-        self.size = np.prod(self.shape)
-        self.real_array = np.arange(self.size).reshape(self.shape)
-
-    def test_real_with_real(self):
-        dm = DataManager(self.real_array * 10)
-        self.assertFalse(dm.has_lazy_data())
-        dm.replace(self.real_array)
-        self.assertFalse(dm.has_lazy_data())
-        self.assertIs(dm._real_array, self.real_array)
-        self.assertIs(dm.data, self.real_array)
-
-    def test_real_with_lazy(self):
-        lazy_array = as_lazy_data(self.real_array)
-        dm = DataManager(self.real_array)
-        self.assertFalse(dm.has_lazy_data())
-        dm.replace(lazy_array)
-        self.assertTrue(dm.has_lazy_data())
-        self.assertIs(dm._lazy_array, lazy_array)
-        self.assertArrayEqual(dm.data, self.real_array)
-
-    def test_lazy_with_real(self):
-        lazy_array = as_lazy_data(self.real_array)
-        dm = DataManager(lazy_array * 10)
-        self.assertTrue(dm.has_lazy_data())
-        dm.replace(self.real_array)
-        self.assertFalse(dm.has_lazy_data())
-        self.assertIs(dm._real_array, self.real_array)
-        self.assertIs(dm.data, self.real_array)
-
-    def test_lazy_with_lazy(self):
-        lazy_array = as_lazy_data(self.real_array)
-        dm = DataManager(lazy_array * 10)
-        self.assertTrue(dm.has_lazy_data())
-        dm.replace(lazy_array)
-        self.assertTrue(dm.has_lazy_data())
-        self.assertIs(dm._lazy_array, lazy_array)
-        self.assertArrayEqual(dm.data, self.real_array)
-
-    def test_lazy_with_real__realised_dtype_none(self):
-        mask_array = ma.arange(self.size).reshape(self.shape)
-        dtype = mask_array.dtype
-        lazy_array = as_lazy_data(mask_array)
-        dm = DataManager(lazy_array, realised_dtype=dtype)
-        self.assertTrue(dm.has_lazy_data())
-        self.assertIsNone(dm._realised_dtype, dtype)
-        self.assertEqual(dm.dtype, dtype)
-        dm.replace(mask_array)
-        self.assertFalse(dm.has_lazy_data())
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, dtype)
-        self.assertIs(dm._real_array, mask_array)
-        self.assertIs(dm.data, mask_array)
-
-    def test_lazy_with_real__realised_dtype_clearance(self):
-        mask_array = ma.arange(self.size).reshape(self.shape)
-        mask_array[0, 0, 0] = ma.masked
-        dtype = mask_array.dtype
-        lazy_array = as_lazy_data(mask_array)
-        dm = DataManager(lazy_array, realised_dtype=dtype)
-        self.assertTrue(dm.has_lazy_data())
-        self.assertEqual(dm._realised_dtype, dtype)
-        self.assertEqual(dm.dtype, dtype)
-        dm.replace(mask_array)
-        self.assertFalse(dm.has_lazy_data())
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, dtype)
-        self.assertIs(dm._real_array, mask_array)
-        self.assertIs(dm.data, mask_array)
-
-    def test_real_with_lazy__realised_dtype_setter_none(self):
-        mask_array = ma.masked_array(self.real_array) * 10
-        dtype = mask_array.dtype
-        lazy_array = as_lazy_data(mask_array)
-        dm = DataManager(self.real_array)
-        self.assertFalse(dm.has_lazy_data())
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, dtype)
-        dm.replace(lazy_array, realised_dtype=dtype)
-        self.assertTrue(dm.has_lazy_data())
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, dtype)
-        self.assertIs(dm._lazy_array, lazy_array)
-        self.assertArrayEqual(dm.data, mask_array)
-
-    def test_real_with_lazy__realised_dtype_setter(self):
-        mask_array = ma.masked_array(self.real_array) * 10
-        mask_array[0, 0, 0] = ma.masked
-        dtype = mask_array.dtype
-        lazy_array = as_lazy_data(mask_array)
-        lazy_dtype = np.dtype('int16')
-        dm = DataManager(self.real_array)
-        self.assertFalse(dm.has_lazy_data())
-        self.assertIsNone(dm._realised_dtype)
-        self.assertEqual(dm.dtype, dtype)
-        dm.replace(lazy_array, realised_dtype=lazy_dtype)
-        self.assertTrue(dm.has_lazy_data())
-        self.assertEqual(dm._realised_dtype, lazy_dtype)
-        self.assertEqual(dm.dtype, lazy_dtype)
-        self.assertIs(dm._lazy_array, lazy_array)
-        self.assertArrayEqual(dm.data, mask_array)
-
-    def test_real_with_real__realised_dtype_failure(self):
-        dm = DataManager(self.real_array)
-        emsg = 'Cannot set realised dtype, no lazy data is available.'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            dm.replace(self.real_array * 10,
-                       realised_dtype=np.dtype('int16'))
-        self.assertIs(dm._real_array, self.real_array)
-        self.assertArrayEqual(dm.data, self.real_array)
-
-    def test_real_with_real__promote_shape_with_dtype_failure(self):
-        data = np.array(666)
-        dm = DataManager(data)
-        emsg = 'Cannot set realised dtype, no lazy data is available'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            dm.replace(np.array([999]),
-                       realised_dtype=np.dtype('float32'))
-        self.assertArrayEqual(dm.data, data)
-
-    def test__clear_fill_value(self):
-        fill_value = 1234
-        dm = DataManager(np.array(0), fill_value=fill_value)
-        self.assertEqual(dm.fill_value, fill_value)
-        dm.replace(np.array(1))
-        self.assertIsNone(dm.fill_value)
-
-    def test__clear_fill_value_masked(self):
-        fill_value = 1234
-        dm = DataManager(np.array(0), fill_value=fill_value)
-        self.assertEqual(dm.fill_value, fill_value)
-        data = ma.masked_array(1, fill_value=4321)
-        dm.replace(data)
-        self.assertIsNone(dm.fill_value)
-
-    def test__set_fill_value(self):
-        fill_value = 1234
-        dm = DataManager(np.array(0))
-        self.assertIsNone(dm.fill_value)
-        dm.replace(np.array(0), fill_value=fill_value)
-        self.assertEqual(dm.fill_value, fill_value)
-
-    def test__set_fill_value_failure(self):
-        dm = DataManager(np.array(0))
-        self.assertIsNone(dm.fill_value)
-        emsg = 'Fill value of .* invalid for dtype'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            dm.replace(np.array(1), fill_value=1e+20)
-
-
 if __name__ == '__main__':
     tests.main()
diff --git a/lib/iris/tests/unit/fileformats/grib/message/test_GribMessage.py b/lib/iris/tests/unit/fileformats/grib/message/test_GribMessage.py
index 3bbd9c8e04..88a7d6d9fb 100644
--- a/lib/iris/tests/unit/fileformats/grib/message/test_GribMessage.py
+++ b/lib/iris/tests/unit/fileformats/grib/message/test_GribMessage.py
@@ -102,8 +102,7 @@ def test_bitmap_present_int_data(self):
                                       6: {'bitMapIndicator': 0,
                                           'bitmap': self.bitmap},
                                       7: {'codedValues': input_values}})
-        result = as_concrete_data(message.data, nans_replacement=ma.masked,
-                                  result_dtype=data_type)
+        result = as_concrete_data(message.data)
         expected = ma.masked_array(output_values,
                                    np.logical_not(self.bitmap))
         expected = expected.reshape(self.shape)
@@ -121,8 +120,7 @@ def test_bitmap_present_float_data(self):
                                       6: {'bitMapIndicator': 0,
                                           'bitmap': self.bitmap},
                                       7: {'codedValues': input_values}})
-        result = as_concrete_data(message.data, nans_replacement=ma.masked,
-                                  result_dtype=data_type)
+        result = as_concrete_data(message.data)
         expected = ma.masked_array(output_values,
                                    np.logical_not(self.bitmap))
         expected = expected.reshape(self.shape)
@@ -137,7 +135,7 @@ def test_bitmap__shapes_mismatch(self):
                                           'bitmap': self.bitmap},
                                       7: {'codedValues': values}})
         with self.assertRaisesRegexp(TranslationError, 'do not match'):
-            as_concrete_data(message.data, nans_replacement=ma.masked)
+            as_concrete_data(message.data)
 
     def test_bitmap__invalid_indicator(self):
         values = np.arange(12)
@@ -146,7 +144,7 @@ def test_bitmap__invalid_indicator(self):
                                           'bitmap': None},
                                       7: {'codedValues': values}})
         with self.assertRaisesRegexp(TranslationError, 'unsupported bitmap'):
-            as_concrete_data(message.data, nans_replacement=ma.masked)
+            as_concrete_data(message.data)
 
 
 class Test_data__unsupported(tests.IrisTest):
diff --git a/lib/iris/tests/unit/fileformats/grib/message/test__DataProxy.py b/lib/iris/tests/unit/fileformats/grib/message/test__DataProxy.py
index 29dcd72120..37b1e38470 100644
--- a/lib/iris/tests/unit/fileformats/grib/message/test__DataProxy.py
+++ b/lib/iris/tests/unit/fileformats/grib/message/test__DataProxy.py
@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2014 - 2016, Met Office
+# (C) British Crown Copyright 2014 - 2017, Met Office
 #
 # This file is part of Iris.
 #
@@ -36,20 +36,20 @@
 class Test__bitmap(tests.IrisTest):
     def test_no_bitmap(self):
         section_6 = {'bitMapIndicator': 255, 'bitmap': None}
-        data_proxy = _DataProxy(0, 0, 0, 0)
+        data_proxy = _DataProxy(0, 0, 0)
         result = data_proxy._bitmap(section_6)
         self.assertIsNone(result)
 
     def test_bitmap_present(self):
         bitmap = randint(2, size=(12))
         section_6 = {'bitMapIndicator': 0, 'bitmap': bitmap}
-        data_proxy = _DataProxy(0, 0, 0, 0)
+        data_proxy = _DataProxy(0, 0, 0)
         result = data_proxy._bitmap(section_6)
         self.assertArrayEqual(bitmap, result)
 
     def test_bitmap__invalid_indicator(self):
         section_6 = {'bitMapIndicator': 100, 'bitmap': None}
-        data_proxy = _DataProxy(0, 0, 0, 0)
+        data_proxy = _DataProxy(0, 0, 0)
         with self.assertRaisesRegexp(TranslationError, 'unsupported bitmap'):
             data_proxy._bitmap(section_6)
 
diff --git a/lib/iris/tests/unit/fileformats/grib/save_rules/test_data_section.py b/lib/iris/tests/unit/fileformats/grib/save_rules/test_data_section.py
index f7985f731f..b617c83d4c 100644
--- a/lib/iris/tests/unit/fileformats/grib/save_rules/test_data_section.py
+++ b/lib/iris/tests/unit/fileformats/grib/save_rules/test_data_section.py
@@ -93,32 +93,6 @@ def test_simple(self):
         # Check the correct data values have been set.
         self.assertValues(grib_api, np.arange(5))
 
-    def test_masked_with_finite_fill_value(self):
-        cube = iris.cube.Cube(np.ma.MaskedArray([1.0, 2.0, 3.0, 1.0, 2.0, 3.0],
-                                                mask=[0, 0, 0, 1, 1, 1]),
-                              fill_value=2000)
-        grib_message = mock.sentinel.GRIB_MESSAGE
-        with mock.patch(GRIB_API) as grib_api:
-            data_section(cube, grib_message)
-        # Check the use of a mask has been turned on.
-        FILL = 2000
-        self.assertBitmapOn(grib_api, FILL)
-        # Check the correct data values have been set.
-        self.assertValues(grib_api, [1, 2, 3, FILL, FILL, FILL])
-
-    def test_masked_with_nan_fill_value(self):
-        cube = iris.cube.Cube(np.ma.MaskedArray([1.0, 2.0, 3.0, 1.0, 2.0, 3.0],
-                                                mask=[0, 0, 0, 1, 1, 1]),
-                              fill_value=np.nan)
-        grib_message = mock.sentinel.GRIB_MESSAGE
-        with mock.patch(GRIB_API) as grib_api:
-            data_section(cube, grib_message)
-        # Check the use of a mask has been turned on and a suitable fill
-        # value has been chosen.
-        FILL = self.assertBitmapRange(grib_api, 1, 3)
-        # Check the correct data values have been set.
-        self.assertValues(grib_api, [1, 2, 3, FILL, FILL, FILL])
-
     def test_scaled(self):
         # If the Cube's units don't match the units required by GRIB
         # ensure the data values are scaled correctly.
@@ -132,39 +106,6 @@ def test_scaled(self):
         # Check the correct data values have been set.
         self.assertValues(grib_api, np.arange(5) * 1000)
 
-    def test_scaled_with_finite_fill_value(self):
-        # When re-scaling masked data with a finite fill value, ensure
-        # the fill value and any filled values are also re-scaled.
-        cube = iris.cube.Cube(np.ma.MaskedArray([1.0, 2.0, 3.0, 1.0, 2.0, 3.0],
-                                                mask=[0, 0, 0, 1, 1, 1]),
-                              standard_name='geopotential_height', units='km',
-                              fill_value=2000)
-        grib_message = mock.sentinel.GRIB_MESSAGE
-        with mock.patch(GRIB_API) as grib_api:
-            data_section(cube, grib_message)
-        # Check the use of a mask has been turned on.
-        FILL = 2000 * 1000
-        self.assertBitmapOn(grib_api, FILL)
-        # Check the correct data values have been set.
-        self.assertValues(grib_api, [1000, 2000, 3000, FILL, FILL, FILL])
-
-    def test_scaled_with_nan_fill_value(self):
-        # When re-scaling masked data with a NaN fill value, ensure
-        # a fill value is chosen which allows for the scaling, and any
-        # filled values match the chosen fill value.
-        cube = iris.cube.Cube(np.ma.MaskedArray([-1.0, 2.0, -1.0, 2.0],
-                                                mask=[0, 0, 1, 1]),
-                              standard_name='geopotential_height', units='km',
-                              fill_value=np.nan)
-        grib_message = mock.sentinel.GRIB_MESSAGE
-        with mock.patch(GRIB_API) as grib_api:
-            data_section(cube, grib_message)
-        # Check the use of a mask has been turned on and a suitable fill
-        # value has been chosen.
-        FILL = self.assertBitmapRange(grib_api, -1000, 2000)
-        # Check the correct data values have been set.
-        self.assertValues(grib_api, [-1000, 2000, FILL, FILL])
-
 
 if __name__ == "__main__":
     tests.main()
diff --git a/lib/iris/tests/unit/fileformats/netcdf/test__load_cube.py b/lib/iris/tests/unit/fileformats/netcdf/test__load_cube.py
index 1e3f0c6e33..1e38baac86 100644
--- a/lib/iris/tests/unit/fileformats/netcdf/test__load_cube.py
+++ b/lib/iris/tests/unit/fileformats/netcdf/test__load_cube.py
@@ -32,83 +32,6 @@
 from iris.tests import mock
 
 
-class TestFillValue(tests.IrisTest):
-    def setUp(self):
-        name = 'iris.fileformats.netcdf._assert_case_specific_facts'
-        patch = mock.patch(name)
-        patch.start()
-        self.addCleanup(patch.stop)
-
-        self.engine = mock.Mock()
-        self.cf = None
-        self.filename = 'DUMMY'
-
-    def _make_cf_var(self, dtype):
-        variable = mock.Mock(spec=netCDF4.Variable,
-                             dtype=dtype)
-        cf_var = mock.MagicMock(spec=iris.fileformats.cf.CFVariable,
-                                cf_data=variable,
-                                cf_name='DUMMY_VAR',
-                                cf_group=mock.Mock(),
-                                dtype=dtype,
-                                shape=(1,))
-        return cf_var
-
-    def _test(self, cf_var, expected_fill_value):
-        cube = _load_cube(self.engine, self.cf, cf_var, self.filename)
-        self.assertEqual(cube.fill_value, expected_fill_value)
-
-    def test_from_attribute_dtype_f4(self):
-        # A _FillValue attribute on the netCDF variable should end up as
-        # the fill_value for the cube.
-        dtype = np.dtype('f4')
-        fill_value = 9999.
-        cf_var = self._make_cf_var(dtype)
-        cf_var.cf_data._FillValue = fill_value
-        self._test(cf_var, fill_value)
-
-    def test_from_default_dtype_f4(self):
-        # Without an explicit _FillValue attribute on the netCDF
-        # variable, the fill value should be set to `None`.
-        dtype = np.dtype('f4')
-        cf_var = self._make_cf_var(dtype)
-        self._test(cf_var, None)
-
-    def test_from_attribute_dtype_i4(self):
-        # A _FillValue attribute on the netCDF variable should end up as
-        # the fill_value for the cube.
-        dtype = np.dtype('i4')
-        fill_value = 9999
-        cf_var = self._make_cf_var(dtype)
-        cf_var.cf_data._FillValue = fill_value
-        self._test(cf_var, fill_value)
-
-    def test_from_default_dtype_i4(self):
-        # Without an explicit _FillValue attribute on the netCDF
-        # variable, the fill value should be set to `None`.
-        dtype = np.dtype('i4')
-        cf_var = self._make_cf_var(dtype)
-        self._test(cf_var, None)
-
-    def test_from_attribute_with_scale_offset(self):
-        # The _FillValue attribute still takes priority even when an
-        # offset/scale transformation takes place on the data.
-        dtype = np.dtype('i2')
-        fill_value = 999
-        cf_var = self._make_cf_var(dtype)
-        cf_var.scale_factor = np.float64(1.5)
-        cf_var.cf_data._FillValue = fill_value
-        self._test(cf_var, fill_value)
-
-    def test_from_default_with_scale_offset(self):
-        # Without an explicit _FillValue attribute on the netCDF
-        # variable, the fill value should be set to `None`.
-        dtype = np.dtype('i2')
-        cf_var = self._make_cf_var(dtype)
-        cf_var.scale_factor = np.float64(1.5)
-        self._test(cf_var, None)
-
-
 class TestCoordAttributes(tests.IrisTest):
     @staticmethod
     def _patcher(engine, cf, cf_group):
diff --git a/lib/iris/tests/unit/fileformats/pp/test_as_pairs.py b/lib/iris/tests/unit/fileformats/pp/test_as_pairs.py
index 7ba752d90f..7f726613a5 100644
--- a/lib/iris/tests/unit/fileformats/pp/test_as_pairs.py
+++ b/lib/iris/tests/unit/fileformats/pp/test_as_pairs.py
@@ -51,8 +51,7 @@ def test_field_coords(self):
     def test_lazy_data(self):
         cube = self.cube.copy()
         # "Rebase" the cube onto a lazy version of its data.
-        cube.replace(cube.lazy_data(), dtype=cube.dtype,
-                     fill_value=cube.fill_value)
+        cube.data = cube.lazy_data()
         # Check that lazy data is preserved in save-pairs generation.
         slices_and_fields = pp.as_pairs(cube)
         for aslice, _ in slices_and_fields:
diff --git a/lib/iris/tests/unit/lazy_data/test_array_masked_to_nans.py b/lib/iris/tests/unit/lazy_data/test_array_masked_to_nans.py
deleted file mode 100644
index cba4ff1cb3..0000000000
--- a/lib/iris/tests/unit/lazy_data/test_array_masked_to_nans.py
+++ /dev/null
@@ -1,111 +0,0 @@
-# (C) British Crown Copyright 2017, Met Office
-#
-# This file is part of Iris.
-#
-# Iris is free software: you can redistribute it and/or modify it under
-# the terms of the GNU Lesser General Public License as published by the
-# Free Software Foundation, either version 3 of the License, or
-# (at your option) any later version.
-#
-# Iris is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU Lesser General Public License for more details.
-#
-# You should have received a copy of the GNU Lesser General Public License
-# along with Iris.  If not, see <http://www.gnu.org/licenses/>.
-"""Test function :func:`iris._lazy data.array_masked_to_nans`."""
-
-from __future__ import (absolute_import, division, print_function)
-from six.moves import (filter, input, map, range, zip)  # noqa
-
-# Import iris.tests first so that some things can be initialised before
-# importing anything else.
-import iris.tests as tests
-
-
-import numpy as np
-import numpy.ma as ma
-
-from iris._lazy_data import array_masked_to_nans
-
-
-class Test(tests.IrisTest):
-    def setUp(self):
-        self.integer_dtypes = (np.dtype('int'),
-                               np.dtype('uint'),
-                               np.dtype('bool'))
-
-    def _common_checks(self, result):
-        self.assertIsInstance(result, np.ndarray)
-        self.assertFalse(ma.isMaskedArray(result))
-
-    def test_masked(self):
-        mask = [[False, True], [False, False]]
-        masked_array = ma.masked_array([[1.0, 2.0], [3.0, 4.0]], mask=mask)
-
-        result = array_masked_to_nans(masked_array)
-
-        self._common_checks(result)
-        self.assertArrayAllClose(np.isnan(result), mask)
-        result[0, 1] = 777.7
-        self.assertArrayAllClose(result, [[1.0, 777.7], [3.0, 4.0]])
-
-    def test_unmasked(self):
-        unmasked_array = np.array([1.0, 2.0])
-        result = array_masked_to_nans(unmasked_array)
-        # Non-masked array is returned as-is, without copying.
-        self.assertIs(result, unmasked_array)
-
-    def test_empty_mask(self):
-        masked_array = ma.masked_array([1.0, 2.0], mask=[0, 0])
-
-        result = array_masked_to_nans(masked_array)
-
-        self._common_checks(result)
-        self.assertArrayAllClose(result, masked_array.data)
-
-    def test_no_mask(self):
-        masked_array = ma.masked_array([1.0, 2.0], mask=ma.nomask)
-
-        result = array_masked_to_nans(masked_array)
-
-        self._common_checks(result)
-        self.assertArrayAllClose(result, masked_array.data)
-
-    def test_masked__integers(self):
-        for dtype in self.integer_dtypes:
-            mask = [[False, True], [False, False]]
-            data = [[1, 2], [3, 4]]
-            masked_array = ma.masked_array(data, mask=mask, dtype=dtype)
-
-            result = array_masked_to_nans(masked_array)
-
-            self._common_checks(result)
-            self.assertEqual(result.dtype, np.dtype('f8'))
-            self.assertArrayAllClose(np.isnan(result), mask)
-            masker = 777.7
-            result[0, 1] = masker
-            expected = np.array(data, dtype=dtype).astype('f8')
-            expected[0, 1] = masker
-            self.assertArrayAllClose(result, expected)
-
-    def test_unmasked__integers(self):
-        for dtype in self.integer_dtypes:
-            unmasked_array = np.array([1, 2], dtype=dtype)
-            result = array_masked_to_nans(unmasked_array)
-            # Non-masked array is returned as-is, without copying.
-            self.assertIs(result, unmasked_array)
-
-    def test_no_mask__integers(self):
-        for dtype in self.integer_dtypes:
-            masked_array = ma.masked_array([1, 2], dtype=dtype, mask=ma.nomask)
-
-            result = array_masked_to_nans(masked_array)
-
-            self._common_checks(result)
-            self.assertEqual(result.dtype, dtype)
-
-
-if __name__ == '__main__':
-    tests.main()
diff --git a/lib/iris/tests/unit/lazy_data/test_as_concrete_data.py b/lib/iris/tests/unit/lazy_data/test_as_concrete_data.py
index 16b0cf7b29..886622f3ab 100644
--- a/lib/iris/tests/unit/lazy_data/test_as_concrete_data.py
+++ b/lib/iris/tests/unit/lazy_data/test_as_concrete_data.py
@@ -27,7 +27,6 @@
 import numpy.ma as ma
 
 from iris._lazy_data import as_concrete_data, as_lazy_data, is_lazy_data
-from iris.tests import mock
 
 
 class Test_as_concrete_data(tests.IrisTest):
@@ -44,49 +43,11 @@ def test_concrete_masked_input_data(self):
         self.assertFalse(is_lazy_data(result))
 
     def test_lazy_data(self):
-        # Minimal testing as as_concrete_data is a wrapper to
-        # convert_nans_array
         data = np.arange(24).reshape((2, 12))
         lazy_array = as_lazy_data(data)
-
-        sentinel = mock.sentinel.data
-        with mock.patch('iris._lazy_data.convert_nans_array') as conv_nans:
-            conv_nans.return_value = sentinel
-            result = as_concrete_data(lazy_array)
-        self.assertEqual(sentinel, result)
-
-        # Check call to convert_nans_array
-        self.assertEqual(conv_nans.call_count, 1)
-        args, kwargs = conv_nans.call_args
-        arg, = args
-        self.assertFalse(is_lazy_data(arg))
-        self.assertArrayEqual(arg, data)
-        self.assertEqual(kwargs, {})
-
-    def test_lazy_data_pass_thru_kwargs(self):
-        # Minimal testing as as_concrete_data is a wrapper to
-        # convert_nans_array
-        data = np.arange(24).reshape((2, 12))
-        lazy_array = as_lazy_data(data)
-        nans_replacement = 7
-        result_dtype = np.int16
-
-        sentinel = mock.sentinel.data
-        with mock.patch('iris._lazy_data.convert_nans_array') as conv_nans:
-            conv_nans.return_value = sentinel
-            result = as_concrete_data(lazy_array,
-                                      nans_replacement=nans_replacement,
-                                      result_dtype=result_dtype)
-        self.assertEqual(sentinel, result)
-
-        # Check call to convert_nans_array
-        self.assertEqual(conv_nans.call_count, 1)
-        args, kwargs = conv_nans.call_args
-        arg, = args
-        self.assertFalse(is_lazy_data(arg))
-        self.assertArrayEqual(arg, data)
-        self.assertEqual(kwargs, {'nans_replacement': nans_replacement,
-                                  'result_dtype': result_dtype, })
+        result = as_concrete_data(lazy_array)
+        self.assertFalse(is_lazy_data(result))
+        self.assertArrayEqual(result, data)
 
 
 if __name__ == '__main__':
diff --git a/lib/iris/tests/unit/lazy_data/test_convert_nans_array.py b/lib/iris/tests/unit/lazy_data/test_convert_nans_array.py
deleted file mode 100644
index f3abb6aaf4..0000000000
--- a/lib/iris/tests/unit/lazy_data/test_convert_nans_array.py
+++ /dev/null
@@ -1,132 +0,0 @@
-# (C) British Crown Copyright 2017, Met Office
-#
-# This file is part of Iris.
-#
-# Iris is free software: you can redistribute it and/or modify it under
-# the terms of the GNU Lesser General Public License as published by the
-# Free Software Foundation, either version 3 of the License, or
-# (at your option) any later version.
-#
-# Iris is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU Lesser General Public License for more details.
-#
-# You should have received a copy of the GNU Lesser General Public License
-# along with Iris.  If not, see <http://www.gnu.org/licenses/>.
-"""
-Test :func:`iris._lazy data.convert_nans_array` function.
-
-"""
-
-from __future__ import (absolute_import, division, print_function)
-from six.moves import (filter, input, map, range, zip)  # noqa
-
-# Import iris.tests first so that some things can be initialised before
-# importing anything else.
-import iris.tests as tests
-
-import numpy as np
-import numpy.ma as ma
-
-from iris._lazy_data import convert_nans_array
-
-
-class Test(tests.IrisTest):
-    def setUp(self):
-        self.array = np.array([[1.0, np.nan],
-                               [3.0, 4.0]])
-
-    def test_pass_thru_masked_array_float(self):
-        array = ma.arange(10, dtype=np.float)
-        result = convert_nans_array(array)
-        self.assertIsInstance(result, ma.MaskedArray)
-        self.assertIs(result, array)
-
-    def test_pass_thru_masked_array_integer(self):
-        array = ma.arange(10)
-        result = convert_nans_array(array)
-        self.assertIsInstance(result, ma.MaskedArray)
-        self.assertIs(result, array)
-
-    def test_pass_thru_array_integer(self):
-        array = np.arange(10)
-        result = convert_nans_array(array)
-        self.assertNotIsInstance(result, ma.MaskedArray)
-        self.assertIs(result, array)
-
-    def test_no_nans(self):
-        array = np.array([[1.0, 2.0],
-                          [3.0, 4.0]])
-        result = convert_nans_array(array)
-        self.assertNotIsInstance(result, ma.MaskedArray)
-        self.assertIs(result, array)
-
-    def test_nans_masked(self):
-        result = convert_nans_array(self.array,
-                                    nans_replacement=ma.masked)
-        self.assertIsInstance(result, ma.MaskedArray)
-        self.assertArrayEqual(result.mask, [[False, True],
-                                            [False, False]])
-        dummy = 666.0
-        result[0, 1] = dummy
-        self.assertArrayEqual(result.data, [[1.0, dummy],
-                                            [3.0, 4.0]])
-        self.assertIsNot(result, self.array)
-        # Check that fill value is the "standard" one for the type.
-        expected = ma.masked_array(self.array[0], dtype=self.array.dtype)
-        self.assertEqual(result.fill_value, expected.fill_value)
-
-    def test_nans_filled(self):
-        fill_value = 666.0
-        result = convert_nans_array(self.array,
-                                    nans_replacement=fill_value)
-        self.assertNotIsInstance(result, ma.MaskedArray)
-        self.assertIs(result, self.array)
-        expected = np.array([[1.0, fill_value],
-                             [3.0, 4.0]])
-        self.assertArrayEqual(result, expected)
-
-    def test_nans_filled_failure(self):
-        fill_value = 1e+20
-        dtype = np.dtype('int16')
-        emsg = 'Fill value of .* invalid for array result .*'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            convert_nans_array(self.array,
-                               nans_replacement=fill_value,
-                               result_dtype=dtype)
-
-    def test_nans_none_failure(self):
-        emsg = 'Array contains unexpected NaNs'
-        with self.assertRaisesRegexp(ValueError, emsg):
-            convert_nans_array(self.array)
-
-    def test_result_dtype_cast_float_to_int(self):
-        dtype = np.int
-        result = convert_nans_array(self.array,
-                                    nans_replacement=ma.masked,
-                                    result_dtype=dtype)
-        self.assertIsInstance(result, ma.MaskedArray)
-        expected = ma.masked_array([[1, 2],
-                                    [3, 4]],
-                                   dtype=dtype)
-        expected[0, 1] = ma.masked
-        self.assertArrayEqual(result, expected)
-        self.assertIsNot(result, self.array)
-
-    def test_filled_result_dtype_cast_float_to_int(self):
-        fill_value = 666
-        dtype = np.int
-        result = convert_nans_array(self.array,
-                                    nans_replacement=fill_value,
-                                    result_dtype=dtype)
-        self.assertNotIsInstance(result, ma.MaskedArray)
-        expected = np.array([[1, fill_value],
-                             [3, 4]],
-                            dtype=dtype)
-        self.assertArrayEqual(result, expected)
-        self.assertIsNot(result, self.array)
-
-
-if __name__ == '__main__':
-    tests.main()
diff --git a/lib/iris/util.py b/lib/iris/util.py
index 4ca915445c..263babac8e 100644
--- a/lib/iris/util.py
+++ b/lib/iris/util.py
@@ -984,8 +984,7 @@ def new_axis(src_cube, scalar_coord=None):
     # If the source cube is a Masked Constant, it is changed here to a Masked
     # Array to allow the mask to gain an extra dimension with the data.
     if src_cube.has_lazy_data():
-        new_cube = iris.cube.Cube(src_cube.lazy_data()[None],
-                                  dtype=src_cube.dtype)
+        new_cube = iris.cube.Cube(src_cube.lazy_data()[None])
     else:
         if isinstance(src_cube.data, ma.core.MaskedConstant):
             new_data = ma.array([np.nan], mask=[True])
@@ -994,7 +993,6 @@ def new_axis(src_cube, scalar_coord=None):
         new_cube = iris.cube.Cube(new_data)
 
     new_cube.metadata = src_cube.metadata
-    new_cube.fill_value = src_cube.fill_value
 
     for coord in src_cube.aux_coords:
         if scalar_coord and scalar_coord == coord:
@@ -1076,9 +1074,7 @@ def as_compatible_shape(src_cube, target_cube):
         new_order = [order.index(i) for i in range(len(order))]
         new_data = np.transpose(new_data, new_order).copy()
 
-    new_cube = iris.cube.Cube(new_data.reshape(new_shape),
-                              fill_value=src_cube.fill_value,
-                              dtype=src_cube.dtype)
+    new_cube = iris.cube.Cube(new_data.reshape(new_shape))
     new_cube.metadata = copy.deepcopy(src_cube.metadata)
 
     # Record a mapping from old coordinate IDs to new coordinates,