diff --git a/.github/workflows/benchmarks_run.yml b/.github/workflows/benchmarks_run.yml
index c91e7841a1..36e7c5e0fb 100644
--- a/.github/workflows/benchmarks_run.yml
+++ b/.github/workflows/benchmarks_run.yml
@@ -66,7 +66,6 @@ jobs:
       IRIS_TEST_DATA_PATH: benchmarks/iris-test-data
       IRIS_TEST_DATA_VERSION: "2.28"
       # Lets us manually bump the cache to rebuild
-      ENV_CACHE_BUILD: "0"
       TEST_DATA_CACHE_BUILD: "2"
 
     steps:
@@ -79,15 +78,10 @@ jobs:
       - name: Install run dependencies
         run: pip install asv nox!=2025.05.01
 
-      - name: Cache environment directories
-        id: cache-env-dir
-        uses: actions/cache@v4
-        with:
-          path: |
-            .nox
-            benchmarks/.asv/env
-            $CONDA/pkgs
-          key: ${{ runner.os }}-${{ hashFiles('requirements/') }}-${{ env.ENV_CACHE_BUILD }}
+      # Note: this cache is shared across workflows, so sets its own cache period
+      #  and build number.
+      - name: Cache Conda package directory
+        uses: ./.github/workflows/composite/conda-pkg-cache
 
       - name: Cache test data directory
         id: cache-test-data
diff --git a/.github/workflows/benchmarks_validate.yml b/.github/workflows/benchmarks_validate.yml
index e3f090b32c..26930b501d 100644
--- a/.github/workflows/benchmarks_validate.yml
+++ b/.github/workflows/benchmarks_validate.yml
@@ -21,10 +21,6 @@ jobs:
   validate:
     runs-on: ubuntu-latest
 
-    env:
-      # Lets us manually bump the cache to rebuild
-      ENV_CACHE_BUILD: "0"
-
     steps:
       - name: Checkout repo
         uses: actions/checkout@v5
@@ -34,15 +30,10 @@ jobs:
       - name: Install run dependencies
         run: pip install asv nox!=2025.05.01
 
-      - name: Cache environment directories
-        id: cache-env-dir
-        uses: actions/cache@v4
-        with:
-          path: |
-            .nox
-            benchmarks/.asv/env
-            $CONDA/pkgs
-          key: ${{ runner.os }}-${{ hashFiles('requirements/') }}-${{ env.ENV_CACHE_BUILD }}
+      # Note: this cache is shared across workflows, so sets its own cache period
+      #  and build number.
+      - name: Cache Conda package directory
+        uses: ./.github/workflows/composite/conda-pkg-cache
 
       - name: Validate setup
         run: nox -s benchmarks -- validate
diff --git a/.github/workflows/ci-tests.yml b/.github/workflows/ci-tests.yml
index 5df55143bd..9cb036031d 100644
--- a/.github/workflows/ci-tests.yml
+++ b/.github/workflows/ci-tests.yml
@@ -73,12 +73,12 @@ jobs:
           env_name: ${{ env.ENV_NAME }}
           version: ${{ env.IRIS_TEST_DATA_VERSION }}
 
+      # Note: this cache is shared across workflows, so sets its own cache period
+      #  and build number.
       - name: "conda package cache"
         uses: ./.github/workflows/composite/conda-pkg-cache
         with:
-          cache_build: 6
-          cache_period: ${{ env.CACHE_PERIOD }}
-          env_name: ${{ env.ENV_NAME }}
+          python_version: ${{ matrix.python-version }}
 
       - name: "conda install"
         uses: conda-incubator/setup-miniconda@v3
@@ -87,14 +87,12 @@ jobs:
           channels: conda-forge
           activate-environment: ${{ env.ENV_NAME }}
           auto-update-conda: false
+          # This aligns the top-level env with the env that Nox will create
+          #  below - meaning optimal use of package caching.
+          python-version: ${{ matrix.python-version }}
 
-      - name: "conda environment cache"
-        uses: ./.github/workflows/composite/conda-env-cache
-        with:
-          cache_build: 6
-          cache_period: ${{ env.CACHE_PERIOD }}
-          env_name: ${{ env.ENV_NAME }}
-          install_packages: "cartopy nox pip"
+      - name: "install cartopy + nox + pip"
+        run: conda install --quiet --name ${{ env.ENV_NAME }} cartopy nox pip
 
       - name: "conda info"
         run: |
@@ -108,13 +106,6 @@ jobs:
           cache_period: ${{ env.CACHE_PERIOD }}
           env_name: ${{ env.ENV_NAME }}
 
-      - name: "nox cache"
-        uses: ./.github/workflows/composite/nox-cache
-        with:
-          cache_build: 6
-          env_name: ${{ env.ENV_NAME }}
-          lock_file: ${{ env.LOCK_FILE }}
-
       # TODO: drop use of site.cfg and explicit use of mplrc
       - name: "iris configure"
         env:
diff --git a/.github/workflows/ci-wheels.yml b/.github/workflows/ci-wheels.yml
index 7d7eea830b..24342c3db4 100644
--- a/.github/workflows/ci-wheels.yml
+++ b/.github/workflows/ci-wheels.yml
@@ -74,36 +74,26 @@ jobs:
         echo "CACHE_PERIOD=$(date +%Y).$(expr $(date +%U) / ${CACHE_WEEKS})" >> ${GITHUB_ENV}
         echo "LOCK_FILE=requirements/locks/py$(echo ${{ matrix.python-version }} | tr -d '.')-linux-64.lock" >> ${GITHUB_ENV}
 
+    # Note: this cache is shared across workflows, so sets its own cache period
+    #  and build number.
     - name: "conda package cache"
       uses: ./.github/workflows/composite/conda-pkg-cache
       with:
-        cache_build: 0
-        cache_period: ${{ env.CACHE_PERIOD }}
-        env_name: ${{ env.ENV_NAME }}
+        python_version: ${{ matrix.python-version }}
 
     - name: "conda install"
       uses: conda-incubator/setup-miniconda@v3
       with:
         miniforge-version: latest
-        channels: conda-forge,defaults
+        channels: conda-forge
         activate-environment: ${{ env.ENV_NAME }}
         auto-update-conda: false
-        use-only-tar-bz2: true
+        # This aligns the top-level env with the env that Nox will create
+        #  below - meaning optimal use of package caching.
+        python-version: ${{ matrix.python-version }}
 
-    - name: "conda environment cache"
-      uses: ./.github/workflows/composite/conda-env-cache
-      with:
-        cache_build: 0
-        cache_period: ${{ env.CACHE_PERIOD }}
-        env_name: ${{ env.ENV_NAME }}
-        install_packages: "nox pip"
-
-    - name: "nox cache"
-      uses: ./.github/workflows/composite/nox-cache
-      with:
-        cache_build: 1
-        env_name: ${{ env.ENV_NAME }}
-        lock_file: ${{ env.LOCK_FILE }}
+    - name: "install nox + pip"
+      run: conda install --quiet --name ${{ env.ENV_NAME }} nox pip
 
     - name: "nox install and test wheel"
       env:
diff --git a/.github/workflows/composite/conda-env-cache/action.yml b/.github/workflows/composite/conda-env-cache/action.yml
deleted file mode 100644
index 15eaaec63c..0000000000
--- a/.github/workflows/composite/conda-env-cache/action.yml
+++ /dev/null
@@ -1,35 +0,0 @@
-name: "conda-env-cache"
-description: "create and cache the conda environment"
-
-#
-# Assumes the environment contains the following variables:
-#   - CONDA
-#
-inputs:
-  cache_build:
-    description: "conda environment cache build number"
-    required: false
-    default: "0"
-  cache_period:
-    description: "conda environment cache timestamp"
-    required: true
-  env_name:
-    description: "environment name"
-    required: true
-  install_packages:
-    description: "conda packages to install into environment"
-    required: true
-
-runs:
-  using: "composite"
-  steps:
-    - uses: actions/cache@v4
-      id: conda-env-cache
-      with:
-        path: ${{ env.CONDA }}/envs/${{ inputs.env_name }}
-        key: ${{ runner.os }}-conda-env-${{ inputs.env_name }}-p${{ inputs.cache_period }}-b${{ inputs.cache_build }}
-
-    - if: steps.conda-env-cache.outputs.cache-hit != 'true'
-      shell: bash
-      run: |
-        conda install --quiet --name ${{ inputs.env_name }} ${{ inputs.install_packages }}
diff --git a/.github/workflows/composite/conda-pkg-cache/action.yml b/.github/workflows/composite/conda-pkg-cache/action.yml
index 48c4470e44..616c76df96 100644
--- a/.github/workflows/composite/conda-pkg-cache/action.yml
+++ b/.github/workflows/composite/conda-pkg-cache/action.yml
@@ -1,22 +1,42 @@
 name: "conda-pkg-cache"
-description: "cache the conda environment packages"
+description: "standardise conda package cache to ~/conda_pkgs_dir and cache across workflow runs"
 
 inputs:
-  cache_build:
-    description: "conda environment cache build number"
+  python_version:
+    description: "conda package cache python version"
     required: false
-    default: "0"
-  cache_period:
-    description: "conda environment cache timestamp"
-    required: true
-  env_name:
-    description: "environment name"
-    required: true
+    default: "3.13"
 
 runs:
   using: "composite"
   steps:
-    - uses: actions/cache@v4
+    - id: set-cache-period
+      shell: bash
+      env:
+        # Maximum cache period (in weeks) before forcing a cache refresh..
+        CACHE_WEEKS: 2
+      run: echo "CACHE_PERIOD=$(date +%Y).$(expr $(date +%U) / ${CACHE_WEEKS})" >> $GITHUB_OUTPUT
+
+    - id: define-cache-key
+      shell: bash
+      env:
+        # Lets us manually bump the cache to rebuild.
+        CACHE_BUILD: "0"
+      run: |
+        OS="${{ runner.os }}"
+        PERIOD="${{ steps.set-cache-period.outputs.CACHE_PERIOD }}"
+        BUILD="${{ env.CACHE_BUILD }}"
+        PY="${{ inputs.python_version }}"
+        REQ="${{ hashFiles('requirements/locks/**') }}"
+        CACHE_KEY="conda_pkgs_dir-${OS}-p${PERIOD}-b${BUILD}-py${PY}-${REQ}"
+        echo "CACHE_KEY=$CACHE_KEY" >> $GITHUB_ENV
+
+    - id: set-pkg-dir
+      shell: bash
+      run: conda config --add pkgs_dirs ~/conda_pkgs_dir
+
+    - id: conda-pkg-cache
+      uses: actions/cache@v4
       with:
         path: ~/conda_pkgs_dir
-        key: ${{ runner.os }}-conda-pkgs-${{ inputs.env_name }}-p${{ inputs.cache_period }}-b${{ inputs.cache_build }}
+        key: ${{ env.CACHE_KEY }}
diff --git a/.github/workflows/composite/nox-cache/action.yml b/.github/workflows/composite/nox-cache/action.yml
deleted file mode 100644
index 00387331e7..0000000000
--- a/.github/workflows/composite/nox-cache/action.yml
+++ /dev/null
@@ -1,22 +0,0 @@
-name: "nox cache"
-description: "cache the nox test environments"
-
-inputs:
-  cache_build:
-    description: "nox cache build number"
-    required: false
-    default: "0"
-  env_name:
-    description: "environment name"
-    required: true
-  lock_file:
-    description: "conda-lock environment requirements filename"
-    required: true
-
-runs:
-  using: "composite"
-  steps:
-    - uses: actions/cache@v4
-      with:
-        path: ${{ github.workspace }}/.nox
-        key: ${{ runner.os }}-nox-${{ inputs.env_name }}-s${{ matrix.session }}-py${{ matrix.python-version }}-b${{ inputs.cache_build }}-${{ hashFiles(inputs.lock_file) }}
diff --git a/lib/iris/tests/test_coding_standards.py b/lib/iris/tests/test_coding_standards.py
index f51a531721..13abceb858 100644
--- a/lib/iris/tests/test_coding_standards.py
+++ b/lib/iris/tests/test_coding_standards.py
@@ -83,6 +83,7 @@ def test_python_versions():
     nox_file = root_dir / "noxfile.py"
     ci_wheels_file = workflows_dir / "ci-wheels.yml"
     ci_tests_file = workflows_dir / "ci-tests.yml"
+    ci_pkg_cache_file = workflows_dir / "composite" / "conda-pkg-cache" / "action.yml"
     benchmark_runner_file = benchmarks_dir / "bm_runner.py"
 
     text_searches: List[Tuple[Path, str]] = [
@@ -107,6 +108,7 @@ def test_python_versions():
                 f'{" " * 8}session: ["doctest", "gallery"]'
             ),
         ),
+        (ci_pkg_cache_file, f'default: "{latest_supported}"'),
         (benchmark_runner_file, f'python_version = "{latest_supported}"'),
     ]