diff --git a/lib/iris/_concatenate.py b/lib/iris/_concatenate.py
index 67a5b90a5e..b6c7bc1cff 100644
--- a/lib/iris/_concatenate.py
+++ b/lib/iris/_concatenate.py
@@ -28,6 +28,7 @@
 
 import dask.array as da
 import numpy as np
+import numpy.ma as ma
 
 import iris.coords
 import iris.cube
@@ -329,6 +330,16 @@ def __init__(self, cube):
 
         self.defn = cube.metadata
         self.data_type = cube.dtype
+        # Concatenation will generate resultant cubes that contain lazy data.
+        # We need to deal with the special case of preserving the dtype of a
+        # candidate cube with concrete masked integral data by ensuring that
+        # the cube metadata has the correct target dtype.
+        kwargs = self.defn._asdict()
+        if kwargs['dtype'] is None and not cube.has_lazy_data() and \
+                isinstance(cube.data, ma.masked_array) and \
+                cube.data.dtype.kind == 'i':
+            kwargs['dtype'] = self.data_type
+            self.defn = iris.cube.CubeMetadata(**kwargs)
 
         #
         # Collate the dimension coordinate metadata.
@@ -402,6 +413,20 @@ def _coordinate_differences(self, other, attr):
                       ', '.join(diff_names))
         return result
 
+    def promote_defn(self):
+        """
+        Update the metadata definition to match that of a similar but lazy
+        cube. A cube with lazy masked integral data must have its
+        :attr:`metadata.dtype` set appropriately.
+
+        """
+        defn = self.defn
+        kwargs = defn._asdict()
+        if kwargs['dtype'] is None and self.data_type.kind == 'i':
+            kwargs['dtype'] = self.data_type
+            defn = iris.cube.CubeMetadata(**kwargs)
+        return defn
+
     def match(self, other, error_on_mismatch):
         """
         Return whether this _CubeSignature equals another.
@@ -433,10 +458,17 @@ def match(self, other, error_on_mismatch):
 
         # Check cube definitions.
         if self.defn != other.defn:
-            # Note that the case of different phenomenon names is dealt with
-            # in :meth:`iris.cube.CubeList.concatenate_cube()`.
-            msg = 'Cube metadata differs for phenomenon: {}'
-            msgs.append(msg.format(self.defn.name()))
+            # Attempt to match metadata for the lazy masked integral
+            # dtype case.
+            promoted = self.promote_defn()
+            if promoted != other.promote_defn():
+                # Note that the case of different phenomenon names is dealt
+                # with in :meth:`iris.cube.CubeList.concatenate_cube()`.
+                msg = 'Cube metadata differs for phenomenon: {}'
+                msgs.append(msg.format(self.defn.name()))
+            else:
+                # Persist the promoted metadata dtype match case.
+                self.defn = promoted
         # Check dim coordinates.
         if self.dim_metadata != other.dim_metadata:
             differences = self._coordinate_differences(other, 'dim_metadata')
diff --git a/lib/iris/analysis/__init__.py b/lib/iris/analysis/__init__.py
index c63cce14b6..9104a96d7c 100644
--- a/lib/iris/analysis/__init__.py
+++ b/lib/iris/analysis/__init__.py
@@ -563,7 +563,9 @@ def post_process(self, collapsed_cube, data_result, coords, **kwargs):
             The collapsed cube with its aggregated data payload.
 
         """
+        cube_fill_value = collapsed_cube.fill_value
         collapsed_cube.data = data_result
+        collapsed_cube.fill_value = cube_fill_value
         return collapsed_cube
 
     def aggregate_shape(self, **kwargs):
diff --git a/lib/iris/cube.py b/lib/iris/cube.py
index 230162c943..0772467ce3 100644
--- a/lib/iris/cube.py
+++ b/lib/iris/cube.py
@@ -65,8 +65,8 @@ class CubeMetadata(collections.namedtuple('CubeMetadata',
                                            'units',
                                            'attributes',
                                            'cell_methods',
-                                           'fill_value',
-                                           'dtype'])):
+                                           'dtype',
+                                           'fill_value'])):
     """
     Represents the phenomenon metadata for a single :class:`Cube`.
 
@@ -751,10 +751,12 @@ def __init__(self, data, standard_name=None, long_name=None,
         # Cell Measures
         self._cell_measures_and_dims = []
 
+        # We need to set the dtype before the fill_value,
+        # as the fill_value is checked against self.dtype.
+        self._dtype = None
+        self.dtype = dtype
         self.fill_value = fill_value
 
-        self._dtype = dtype
-
         identities = set()
         if dim_coords_and_dims:
             dims = set()
@@ -798,7 +800,7 @@ def metadata(self):
         """
         return CubeMetadata(self.standard_name, self.long_name, self.var_name,
                             self.units, self.attributes, self.cell_methods,
-                            self.fill_value, self._dtype)
+                            self._dtype, self.fill_value)
 
     @metadata.setter
     def metadata(self, value):
@@ -813,7 +815,10 @@ def metadata(self, value):
                 if missing_attrs:
                     raise TypeError('Invalid/incomplete metadata')
         for name in CubeMetadata._fields:
-            setattr(self, name, getattr(value, name))
+            alias = name
+            if name in ['dtype', 'fill_value']:
+                alias = '_{}'.format(name)
+            setattr(self, alias, getattr(value, name))
 
     def is_compatible(self, other, ignore=None):
         """
@@ -1632,7 +1637,38 @@ def dtype(self):
 
     @dtype.setter
     def dtype(self, dtype):
-        self._dtype = dtype
+        if dtype != self.dtype:
+            if dtype is not None:
+                if not self.has_lazy_data():
+                    emsg = 'Cube does not have lazy data, cannot set dtype.'
+                    raise ValueError(emsg)
+                dtype = np.dtype(dtype)
+                if dtype.kind != 'i':
+                    emsg = ('Can only cast lazy data to integral dtype, '
+                            'got {!r}.')
+                    raise ValueError(emsg.format(dtype))
+                self._fill_value = None
+            self._dtype = dtype
+
+    @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 cube.
+            fill_value = np.asarray([fill_value])[0]
+            target_dtype = self.dtype
+            if fill_value.dtype.kind == 'f' and target_dtype.kind == 'i':
+                # 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 cube {!r}.'
+                raise ValueError(emsg.format(fill_value, self.dtype))
+        self._fill_value = fill_value
 
     @property
     def ndim(self):
@@ -1731,12 +1767,17 @@ def data(self, value):
                 raise ValueError('Require cube data with shape %r, got '
                                  '%r.' % (self.shape, value.shape))
 
+        # Set lazy or real data, and reset the other.
         if is_lazy_data(value):
             self._dask_array = value
             self._numpy_array = None
-
         else:
             self._numpy_array = value
+            self._dask_array = None
+
+        # Cancel any 'realisation' datatype conversion, and fill value.
+        self.dtype = None
+        self.fill_value = None
 
     def has_lazy_data(self):
         return self._numpy_array is None
diff --git a/lib/iris/tests/results/FF/air_temperature_1.cml b/lib/iris/tests/results/FF/air_temperature_1.cml
index 2bd0d3f4e2..8d653c28e9 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="-1073741824.0" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" 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 e06cf23ba6..d06ff4d286 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="-1073741824.0" standard_name="air_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" 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 fc221639cf..2549b1b962 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="-1073741824.0" standard_name="soil_temperature" units="K">
+  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" 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 4bd5de8cf4..8ec0c305da 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="-1073741824.0" standard_name="surface_altitude" units="m">
+  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" 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/addition_coord_x.cml b/lib/iris/tests/results/analysis/addition_coord_x.cml
index 4898dd6b58..70c95763b9 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="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1e+30" 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 7404a13def..065e034a86 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="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1e+30" 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_frompyfunc.cml b/lib/iris/tests/results/analysis/apply_ifunc_frompyfunc.cml
index b71ae08a48..73aa603992 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="float32" fill_value="-1e+30" units="kelvin^2">
+  <cube core-dtype="object" dtype="object" fill_value="-1e+30" 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 e33a79366d..fc7cce9134 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="float32" fill_value="-1e+30" units="unknown">
+  <cube core-dtype="object" dtype="object" fill_value="-1e+30" 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/division_by_singular_coord.cml b/lib/iris/tests/results/analysis/division_by_singular_coord.cml
index 7022d4a6e7..c099becdd7 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="float32" fill_value="-1e+30" units="kelvin">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1e+30" 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 caad13a501..62f4bf08ab 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="float32" fill_value="-1e+30" units="kelvin^4">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1.00000001505e+30" 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 400be996bc..e71bb14e74 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 9a934998d4..1176acb50c 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 b4e8361cd5..ac4ed1681d 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 634de70f23..6cc2242648 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 7c214c8e53..2abf38fef2 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 15c5ed7729..931e8c0a97 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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.cml b/lib/iris/tests/results/analysis/max_latitude.cml
index 415373ecd2..b9acb2e1a0 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 988e92e954..623d412a61 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 6fc4129371..f432a91b37 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 58e373ed0c..0317e2b1e2 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 ecf1fa35d2..a45e0a610e 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 4736766c16..44f9930efd 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 e9c4b94141..b43235dd05 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 ef4e733654..4e1335e64b 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 f9850bbfb5..f617c0895f 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 9805d47cc9..7cf5ac7130 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 d68688ea45..0f4087c17c 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 d6a17ea484..cb6d0f200d 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 e29c9e5d27..2b7643b909 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 15430608c1..f342ccc1b7 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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.cml b/lib/iris/tests/results/analysis/rms_latitude.cml
index 9dca51adf3..f134bece0c 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 6a87628f94..16fcffe176 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 4e511c53f7..8c18d225bf 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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.cml b/lib/iris/tests/results/analysis/std_dev_latitude.cml
index 1e04a97d2e..f5c5ee6634 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 f69b1b4319..cc75ca3b56 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 45596e7b6c..50f54f537a 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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_coord_x.cml b/lib/iris/tests/results/analysis/subtract_coord_x.cml
index 7e21df3aa5..855c700c3d 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="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1e+30" 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 0c0e574eb1..c4d695a9da 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="float32" fill_value="-1e+30" units="K">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1e+30" 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 538896df3d..3d1e13a955 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 69994b84dc..4135f70210 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 90164b36d9..d7f26a82f8 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="Pa">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 2759e37577..91921d0e79 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="meter^-2-kilogram^2-second^-4">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 8122c7ff22..82ef78a4ee 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="meter^-4-kilogram^4-second^-8">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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 5485529342..531ec056b7 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="float32" fill_value="-1.07374e+09" standard_name="air_pressure_at_sea_level" units="meter^-2-kilogram^2-second^-4">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1073741824.0" 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/experimental/fieldsfile/TestStructuredLoadFF/simple.cml b/lib/iris/tests/results/experimental/fieldsfile/TestStructuredLoadFF/simple.cml
index d337f92dd5..5cb0de933c 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="-1073741824.0" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" 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 88a433f8f5..62126aa03b 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="-1073741824.0" standard_name="air_pressure" units="Pa">
+  <cube core-dtype="float32" dtype="float32" fill_value="-1.07374e+09" 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/netcdf/netcdf_deferred_index_0.cml b/lib/iris/tests/results/netcdf/netcdf_deferred_index_0.cml
index 17455a2ccf..9e03a24a45 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 0e3627b8b4..eb1e569293 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 fbc9b2796a..d8d9488a0e 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 432a8015f6..4acbce1110 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 0707c01f14..72ac649c0a 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 74ca04cffb..486ca6377a 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 c6cdb691a2..d01cc81467 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 b3781ef07b..0da72836a6 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 bd146e039f..760313769a 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 d016ce9a53..f1779f48eb 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 ed60db2872..d035b1bb6e 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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_total.cml b/lib/iris/tests/results/netcdf/netcdf_global_xyt_total.cml
index 6b20b31434..0d685802ca 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" long_name="Total column Carbon Dioxide" units="kg m**-2" var_name="tcco2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 2e0e257629..b94a1e78a3 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" long_name="Carbon Dioxide" units="kg kg**-1" var_name="co2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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" long_name="Logarithm of surface pressure" units="no_unit" var_name="lnsp">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 33f1a0571f..8a61b31886 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" long_name="Carbon Dioxide" units="kg kg**-1" var_name="co2">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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 c03d47a21d..cb0ce6d5fd 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" long_name="Logarithm of surface pressure" units="no_unit" var_name="lnsp">
+  <cube core-dtype="float64" dtype="float64" fill_value="-32767.0" 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/trajectory/constant_latitude.cml b/lib/iris/tests/results/trajectory/constant_latitude.cml
index 7d9eb06563..8d6caae0ba 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="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1.07374e+09" 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 9328b1c586..28e9480e62 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="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1.07374e+09" 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 0437df1f58..1cfac803d4 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="float32" fill_value="9.96921e+36" long_name="Temperature" standard_name="sea_water_potential_temperature" units="degC" var_name="votemper">
+  <cube core-dtype="float64" dtype="float64" fill_value="9.96921e+36" 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 8bf4213781..e78cc1ffe5 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="float32" fill_value="-1.07374e+09" standard_name="air_potential_temperature" units="K">
+  <cube core-dtype="float64" dtype="float64" fill_value="-1.07374e+09" 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/test_analysis.py b/lib/iris/tests/test_analysis.py
index c496fd5774..8f0cdc8204 100644
--- a/lib/iris/tests/test_analysis.py
+++ b/lib/iris/tests/test_analysis.py
@@ -192,10 +192,12 @@ 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))
 
@@ -221,6 +223,7 @@ 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 abf4a175ea..8e2e64f6da 100644
--- a/lib/iris/tests/test_basic_maths.py
+++ b/lib/iris/tests/test_basic_maths.py
@@ -39,7 +39,11 @@
 class TestBasicMaths(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_abs(self):
         a = self.cube
@@ -360,7 +364,11 @@ 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
@@ -428,7 +436,7 @@ def test_divide_by_coordinate_dim2(self):
         # Check that the division has had no effect on the original
         self.assertCML(a, ('analysis', 'maths_original.cml'))
 
-    def test_divide_by_singluar_coordinate(self):
+    def test_divide_by_singular_coordinate(self):
         a = self.cube
 
         coord = iris.coords.DimCoord(points=2, long_name='foo', units='1')
@@ -503,11 +511,17 @@ def test_type_error(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'))
 
@@ -515,6 +529,8 @@ 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 19b59f294a..db0b0b9696 100644
--- a/lib/iris/tests/test_cdm.py
+++ b/lib/iris/tests/test_cdm.py
@@ -791,7 +791,7 @@ def test_metadata_nop(self):
 
     def test_metadata_tuple(self):
         metadata = ('air_pressure', 'foo', 'bar', '', {'random': '12'}, (),
-                    -99, np.dtype('f8'))
+                    np.dtype('f8'), -99)
         self.t.metadata = metadata
         self.assertEqual(self.t.standard_name, 'air_pressure')
         self.assertEqual(self.t.long_name, 'foo')
diff --git a/lib/iris/tests/test_concatenate.py b/lib/iris/tests/test_concatenate.py
index 260261236f..e644870065 100644
--- a/lib/iris/tests/test_concatenate.py
+++ b/lib/iris/tests/test_concatenate.py
@@ -35,7 +35,8 @@
 
 
 def _make_cube(x, y, data, aux=None, offset=0, scalar=None,
-               dtype=np.dtype('float32'), fill_value=None):
+               dtype=np.dtype('float32'), fill_value=None,
+               mask=None):
     """
     A convenience test function that creates a custom 2D cube.
 
@@ -67,6 +68,10 @@ def _make_cube(x, y, data, aux=None, offset=0, scalar=None,
     * scalar:
         Create a 'height' scalar coordinate with the given value.
 
+    * mask:
+        Create cube masked data with the specified mask. Boolean or
+        array indicies of points to be masked.
+
     Returns:
         The newly created 2D :class:`iris.cube.Cube`.
 
@@ -75,10 +80,19 @@ def _make_cube(x, y, data, aux=None, offset=0, scalar=None,
     y_range = np.arange(*y, dtype=dtype)
     x_size = len(x_range)
     y_size = len(y_range)
+    shape = (y_size, x_size)
 
-    cube_data = np.empty((y_size, x_size), dtype=dtype)
-    cube_data[:] = data
-    cube = iris.cube.Cube(cube_data, fill_value=fill_value, dtype=dtype)
+    if mask is not None:
+        cube_data = ma.empty(shape, dtype=dtype)
+        cube_data.data[:] = data
+        if isinstance(mask, bool):
+            cube_data.mask = mask
+        else:
+            cube_data[mask] = ma.masked
+    else:
+        cube_data = np.empty(shape, dtype=dtype)
+        cube_data[:] = data
+    cube = iris.cube.Cube(cube_data, fill_value=fill_value)
     coord = DimCoord(y_range, long_name='y')
     coord.guess_bounds()
     cube.add_dim_coord(coord, 0)
@@ -217,15 +231,18 @@ 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):
-            # cube.data = ma.copy(cube.data, order=order)
             data = np.array(cube.data.data, copy=True, order=order)
             mask = np.array(cube.data.mask, copy=True, order=order)
-            fill_value = cube.data.fill_value
-            cube.data = ma.array(data, mask=mask, fill_value=fill_value)
+            cube.data = ma.array(data, mask=mask)
         else:
-            # cube.data = np.copy(cube.data, order=order)
             cube.data = np.array(cube.data, copy=True, order=order)
+        cube.fill_value = fill_value
 
     return result
 
@@ -310,7 +327,7 @@ def test_uncommon(self):
         result = concatenate(cubes)
         self.assertEqual(len(result), 2)
 
-    def test_order(self):
+    def test_order_difference(self):
         cubes = []
         y = (0, 2)
         cubes.append(_make_cube((0, 2), y, 1))
@@ -318,42 +335,78 @@ def test_order(self):
         result = concatenate(cubes)
         self.assertEqual(len(result), 2)
 
+    def test_masked_fill_value_difference(self):
+        cubes = []
+        y = (0, 2)
+        cube = _make_cube((0, 2), y, 1, mask=True)
+        cube.fill_value = 10
+        cubes.append(cube)
+        cube = _make_cube((2, 4), y, 1, mask=True)
+        cube.fill_value = 20
+        cubes.append(cube)
+        result = concatenate(cubes)
+        self.assertEqual(len(result), 2)
+
+
+class Test2D(tests.IrisTest):
     def test_masked_and_unmasked(self):
+        cubes = []
+        y = (0, 2)
+        cube = _make_cube((0, 2), y, 1, mask=True)
+        cubes.append(cube)
+        cubes.append(_make_cube((2, 4), y, 2))
+        result = concatenate(cubes)
+        self.assertEqual(len(result), 1)
+
+    def test_masked_and_unmasked_int16(self):
+        cubes = []
+        y = (0, 2)
+        dtype = np.dtype('int16')
+        cube = _make_cube((0, 2), y, 1, dtype=dtype, mask=True)
+        cubes.append(cube)
+        cubes.append(_make_cube((2, 4), y, 2, dtype=dtype))
+        result = concatenate(cubes)
+        self.assertEqual(len(result), 1)
+
+    def test_unmasked_and_masked(self):
         cubes = []
         y = (0, 2)
         cubes.append(_make_cube((0, 2), y, 1))
-        cube = _make_cube((2, 4), y, 2)
-        cube.data = ma.asarray(cube.data)
+        cube = _make_cube((2, 4), y, 2, mask=True)
+        cubes.append(cube)
+        result = concatenate(cubes)
+        self.assertEqual(len(result), 1)
+
+    def test_unmasked_and_masked_int16(self):
+        cubes = []
+        y = (0, 2)
+        dtype = np.dtype('int16')
+        cubes.append(_make_cube((0, 2), y, 1, dtype=dtype))
+        cube = _make_cube((2, 4), y, 2, dtype=dtype, mask=True)
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertEqual(len(result), 1)
 
-    def test_masked_fill_value(self):
+    def test_masked_with_data_fill_value_difference(self):
         cubes = []
         y = (0, 2)
-        cube = _make_cube((0, 2), y, 1)
-        cube.data = ma.asarray(cube.data)
+        cube = _make_cube((0, 2), y, 1, mask=True)
         cube.data.fill_value = 10
         cubes.append(cube)
-        cube = _make_cube((2, 4), y, 1)
-        cube.data = ma.asarray(cube.data)
+        cube = _make_cube((2, 4), y, 1, mask=True)
         cube.data.fill_value = 20
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertEqual(len(result), 1)
 
-
-class Test2D(tests.IrisTest):
     def test_concat_masked_2x2d(self):
         cubes = []
         y = (0, 2)
-        cube = _make_cube((0, 2), y, 1)
-        cube.data = ma.asarray(cube.data)
-        cube.data[(0, 1), (0, 1)] = ma.masked
+        mask = [(0, 1), (0, 1)]
+        cube = _make_cube((0, 2), y, 1, mask=mask)
         cubes.append(cube)
-        cube = _make_cube((2, 4), y, 2)
-        cube.data = ma.asarray(cube.data)
-        cube.data[(0, 1), (1, 0)] = ma.masked
+        mask = [(0, 1), (1, 0)]
+        cube = _make_cube((2, 4), y, 2, mask=mask)
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertCML(result, ('concatenate', 'concat_masked_2x2d.cml'))
@@ -366,13 +419,11 @@ def test_concat_masked_2x2d(self):
     def test_concat_masked_2y2d(self):
         cubes = []
         x = (0, 2)
-        cube = _make_cube(x, (0, 2), 1)
-        cube.data = np.ma.asarray(cube.data)
-        cube.data[(0, 1), (0, 1)] = ma.masked
+        mask = [(0, 1), (0, 1)]
+        cube = _make_cube(x, (0, 2), 1, mask=mask)
         cubes.append(cube)
-        cube = _make_cube(x, (2, 4), 2)
-        cube.data = ma.asarray(cube.data)
-        cube.data[(0, 1), (1, 0)] = ma.masked
+        mask = [(0, 1), (1, 0)]
+        cube = _make_cube(x, (2, 4), 2, mask=mask)
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertCML(result, ('concatenate', 'concat_masked_2y2d.cml'))
@@ -387,15 +438,65 @@ def test_concat_masked_2y2d(self):
     def test_concat_masked_2y2d_int16(self):
         cubes = []
         x = (0, 2)
-        cube = _make_cube(x, (0, 2), 1, dtype=np.dtype('int16'),
-                          fill_value=-37)
-        cube.data = np.ma.asarray(cube.data)
-        cube.data[(0, 1), (0, 1)] = ma.masked
+        dtype = np.dtype('int16')
+        fill_value = -37
+        mask = [(0, 1), (0, 1)]
+        cube = _make_cube(x, (0, 2), 1, dtype=dtype, fill_value=fill_value,
+                          mask=mask)
+        cubes.append(cube)
+        mask = [(0, 1), (1, 0)]
+        cube = _make_cube(x, (2, 4), 2, dtype=dtype, fill_value=fill_value,
+                          mask=mask)
+        cubes.append(cube)
+        result = concatenate(cubes)
+        self.assertCML(result, ('concatenate', 'concat_masked_2y2d_int16.cml'))
+        self.assertEqual(len(result), 1)
+        self.assertEqual(result[0].shape, (4, 2))
+        mask = np.array([[True, False],
+                         [False, True],
+                         [False, True],
+                         [True, False]], dtype=np.bool)
+        self.assertArrayEqual(result[0].data.mask, mask)
+
+    def test_concat_masked_2y2d_int16_with_concrete_and_lazy(self):
+        cubes = []
+        x = (0, 2)
+        dtype = np.dtype('int16')
+        fill_value = -37
+        mask = [(0, 1), (0, 1)]
+        cube = _make_cube(x, (0, 2), 1, dtype=dtype, fill_value=fill_value,
+                          mask=mask)
+        cubes.append(cube)
+        mask = [(0, 1), (1, 0)]
+        cube = _make_cube(x, (2, 4), 2, dtype=dtype, mask=mask)
+        cube.data = cube.lazy_data()
+        cube.dtype = dtype
+        cube.fill_value = fill_value
+        cubes.append(cube)
+        result = concatenate(cubes)
+        self.assertCML(result, ('concatenate', 'concat_masked_2y2d_int16.cml'))
+        self.assertEqual(len(result), 1)
+        self.assertEqual(result[0].shape, (4, 2))
+        mask = np.array([[True, False],
+                         [False, True],
+                         [False, True],
+                         [True, False]], dtype=np.bool)
+        self.assertArrayEqual(result[0].data.mask, mask)
+
+    def test_concat_masked_2y2d_int16_with_lazy_and_concrete(self):
+        cubes = []
+        x = (0, 2)
+        dtype = np.dtype('int16')
+        fill_value = -37
+        mask = [(0, 1), (1, 0)]
+        cube = _make_cube(x, (2, 4), 2, dtype=dtype, mask=mask)
+        cube.data = cube.lazy_data()
+        cube.dtype = dtype
+        cube.fill_value = fill_value
         cubes.append(cube)
-        cube = _make_cube(x, (2, 4), 2, dtype=np.dtype('int16'),
-                          fill_value=-37)
-        cube.data = ma.asarray(cube.data)
-        cube.data[(0, 1), (1, 0)] = ma.masked
+        mask = [(0, 1), (0, 1)]
+        cube = _make_cube(x, (0, 2), 1, dtype=dtype, fill_value=fill_value,
+                          mask=mask)
         cubes.append(cube)
         result = concatenate(cubes)
         self.assertCML(result, ('concatenate', 'concat_masked_2y2d_int16.cml'))
diff --git a/lib/iris/tests/test_interpolation.py b/lib/iris/tests/test_interpolation.py
index f3648e3297..bf537477bc 100644
--- a/lib/iris/tests/test_interpolation.py
+++ b/lib/iris/tests/test_interpolation.py
@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2010 - 2016, Met Office
+# (C) British Crown Copyright 2010 - 2017, Met Office
 #
 # This file is part of Iris.
 #
@@ -26,7 +26,6 @@
 import iris.tests as tests
 
 import numpy as np
-import numpy.ma as ma
 from scipy.interpolate import interp1d
 
 import iris
@@ -43,7 +42,9 @@ def normalise_order(cube):
     #     function when the circular flag is true.
     #   * scipy.interpolate.interp1d in 0.11.0 which is used in
     #     `Linear1dExtrapolator`.
+    cube_fill_val = cube.fill_value
     cube.data = np.ascontiguousarray(cube.data)
+    cube.fill_value = cube_fill_val
 
 
 class TestLinearExtrapolator(tests.IrisTest):
diff --git a/lib/iris/tests/test_pp_cf.py b/lib/iris/tests/test_pp_cf.py
index 430f01123d..39227fb82e 100644
--- a/lib/iris/tests/test_pp_cf.py
+++ b/lib/iris/tests/test_pp_cf.py
@@ -80,6 +80,8 @@ def callback_aaxzc_n10r13xy_b_pp(cube, field, filename):
     cube.add_aux_coord(height_coord)
 
 
+# XXX: Issue with integer.b.pp and invalid bmdi fill_value for int32 dtype
+@tests.skip_biggus
 @tests.skip_data
 class TestAll(tests.IrisTest, pp.PPTest):
     _ref_dir = ('usecases', 'pp_to_cf_conversion')
diff --git a/lib/iris/tests/unit/analysis/regrid/test_RectilinearRegridder.py b/lib/iris/tests/unit/analysis/regrid/test_RectilinearRegridder.py
index 243a1579fb..b181676e01 100644
--- a/lib/iris/tests/unit/analysis/regrid/test_RectilinearRegridder.py
+++ b/lib/iris/tests/unit/analysis/regrid/test_RectilinearRegridder.py
@@ -1262,7 +1262,9 @@ def test_circular_src__masked_missingmask(self):
         # instead of being an array.
         src = self.src
         src.coord('longitude').circular = True
+        src_fill_value = src.fill_value
         src.data = np.ma.MaskedArray(src.data)
+        src.fill_value = src_fill_value
         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/cube/test_Cube.py b/lib/iris/tests/unit/cube/test_Cube.py
index 849491fc19..9260d8dc86 100644
--- a/lib/iris/tests/unit/cube/test_Cube.py
+++ b/lib/iris/tests/unit/cube/test_Cube.py
@@ -1240,6 +1240,175 @@ def test_lazy(self):
         self.assertTrue(cube.has_lazy_data())
 
 
+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 = np.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.
+        cube = self._sample_cube(cube_fill_value=27.3, masked=True, lazy=True)
+        data = cube.data
+        self.assertIs(cube.core_data, data)
+        self.assertArrayAllClose(cube.fill_value, 27.3)
+
+    def test_realise_maskedints(self):
+        # Check that touching masked integer lazy data retains the fill_value.
+        cube = self._sample_cube(dtype=np.int16, masked=True, lazy=True,
+                                 cube_fill_value=999)
+        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, 999)
+
+    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_realdata_dtype_change(self):
+        # Check that cannot change real data dtype.
+        cube = self._sample_cube()
+        with self.assertRaisesRegexp(ValueError, "cannot set dtype"):
+            cube.dtype = np.dtype('i8')
+
+    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 that lazy masked ints have a modified dtype.
+        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)
+        cube.dtype = masked_data_original.dtype
+        self.assertEqual(cube.dtype, np.dtype('i4'))
+        self.assertEqual(cube.core_data.dtype, np.dtype('f8'))
+        data = cube.data
+        self.assertTrue(np.ma.is_masked(data))
+        self.assertMaskedArrayEqual(data, masked_data_original)
+
+    def test_lazydata_floating_dtype_change(self):
+        # Check that re-assigning dtype won't allow a floating type.
+        cube = self._sample_cube(dtype=np.float32, lazy=True,
+                                 cube_fill_value=23.7)
+        self.assertArrayAllClose(cube.fill_value, 23.7)
+        msg = "Can only cast lazy data to integral dtype"
+        with self.assertRaisesRegexp(ValueError, msg):
+            cube.dtype = np.float64
+
+    def test_lazydata_dtype_change(self):
+        # Check that re-assigning dtype resets fill_value.
+        cube = self._sample_cube(dtype=np.float32, lazy=True,
+                                 cube_fill_value=23.7)
+        self.assertArrayAllClose(cube.fill_value, 23.7)
+        cube.dtype = np.int16
+        self.assertEqual(cube.dtype, np.dtype('i2'))
+        self.assertEqual(cube.core_data.dtype, np.dtype('f4'))
+        self.assertIsNone(cube.fill_value)
+
+    def test_lazydata_maskedints_dtype_change(self):
+        # Check that re-assigning dtype resets fill_value.
+        cube = self._sample_cube(dtype=np.int16, masked=True, lazy=True,
+                                 cube_fill_value=199)
+        self.assertEqual(cube.dtype, np.dtype('i2'))
+        self.assertEqual(cube.core_data.dtype, np.dtype('f8'))
+        self.assertArrayAllClose(cube.fill_value, 199)
+        cube.dtype = np.int64
+        self.assertEqual(cube.dtype, np.dtype('i8'))
+        self.assertEqual(cube.core_data.dtype, np.dtype('f8'))
+        self.assertIsNone(cube.fill_value)
+
+    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 = "invalid for cube 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)
+
+
 class TestSubset(tests.IrisTest):
     def test_scalar_coordinate(self):
         cube = Cube(0, long_name='apricot', units='1')
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 56480de793..8666c39cab 100644
--- a/lib/iris/tests/unit/fileformats/netcdf/test__load_cube.py
+++ b/lib/iris/tests/unit/fileformats/netcdf/test__load_cube.py
@@ -139,7 +139,7 @@ def _make(self, names, attrs):
 
         cf_var = mock.MagicMock(spec=iris.fileformats.cf.CFVariable,
                                 dtype=np.dtype('i4'),
-                                cf_data=mock.Mock(),
+                                cf_data=mock.Mock(_FillValue=None),
                                 cf_name='DUMMY_VAR',
                                 cf_group=coords,
                                 shape=(1,))