diff --git a/noxfile.py b/noxfile.py
index fc6175bdf0..92a892a3c3 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -165,6 +165,11 @@ def tests(session):
 
     cache_cartopy(session)
     session.install("--no-deps", "--editable", ".")
+
+    # Always echo the env content for CI test failure debugging.
+    session.install("beautifultable")
+    session.run("python", "tools/env_listing.py")
+
     session.run(
         "python",
         "-m",
diff --git a/tools/env_listing.py b/tools/env_listing.py
new file mode 100644
index 0000000000..a54bb947b7
--- /dev/null
+++ b/tools/env_listing.py
@@ -0,0 +1,130 @@
+# Copyright Iris contributors
+#
+# This file is part of Iris and is released under the LGPL license.
+# See COPYING and COPYING.LESSER in the root of the repository for full
+# licensing details.
+"""
+Produce a listing output of the calling Python environment.
+
+Combine "conda list" with a "pip list" to describe all installed packages.
+
+"""
+from subprocess import check_output
+import beautifultable as bt
+
+
+def sanitise_lines(lines, header_line_hint=None):
+    """
+    Split string by spaces, removing leading, trailing and repeated whitespace.
+    Remove header lines up to the last one containing 'header_line_hint'.
+
+    """
+    pkg_info = []
+    for line in lines:
+        line = line.strip()
+        while '\t' in line:
+            line = line.replace('\t', ' ')
+        while '  ' in line:
+            ...
+            line = line.replace('  ', ' ')
+        line = line.split(' ')
+        if len(line) > 0 and line[0] not in ('', '#'):
+            pkg_info.append(line)
+
+    pkg_keys = [pkg[0] for pkg in pkg_info]
+    if header_line_hint is not None:
+        header_inds = [ind for ind, key in enumerate(pkg_keys)
+                       if header_line_hint in key]
+        if len(header_inds) > 0:
+            pkg_info = pkg_info[header_inds[-1] + 1:]
+
+    result = {pkg[0]: pkg[1:] for pkg in pkg_info}
+    return result
+
+
+def scan_env():
+    """
+    Get package listings from conda and pip.
+
+    Return:
+        package_names, conda_info, pip_info
+
+    The package names are sorted.
+    'pip_info' is a dict : name --> version
+    'conda_info' is a dict : name --> version, build, channel
+    Any package may be present in either dict, or both.
+
+    """
+    conda_list_bytes = check_output(['conda list'], shell=True)
+    conda_list_lines = conda_list_bytes.decode().split('\n')
+    pip_list_bytes = check_output(['pip list'], shell=True)
+    pip_list_lines = pip_list_bytes.decode().split('\n')
+
+    conda_info = sanitise_lines(conda_list_lines)
+    pip_info = sanitise_lines(pip_list_lines, header_line_hint='---')
+    conda_keys = set(conda_info.keys())
+    pip_keys = set([pkg[0] for pkg in pip_info])
+    all_keys = sorted(set(conda_info.keys()) | set(pip_info.keys()))
+
+    return all_keys, conda_info, pip_info
+
+
+def make_package_table(package_names, conda_info, pip_info):
+    """
+    Turn the package info returned from 'scan_env' into a printable table.
+
+    """
+    table = bt.BeautifulTable()
+    table.columns.header = [
+        'Package', 'source', 'version(s)', 'conda-version', 'conda-channel']
+
+    def version_summary(package, pip_info, conda_info):
+        """
+        Extract + combine info from pip and conda about 'package'.
+        Return a list of 5 strings :  package, source, version, build, channel.
+
+        """
+        pipver = pip_info[package][0] if package in pip_info else None
+        condaver = conda_info[package][0] if package in conda_info else None
+        columns = [package] + [''] * 4
+        if condaver:
+            conda_extra_columns = conda_info[package][1:]
+            # Normally will get ", build, channel'
+            # But it seems we may need to allow for more or less.
+            while len(conda_extra_columns) < 2:
+                conda_extra_columns += ['']
+            if len(conda_extra_columns) > 2:
+                conda_extra_columns[1] = ' '.join(conda_extra_columns[1:])
+                conda_extra_columns = conda_extra_columns[:2]
+            assert len(conda_extra_columns) == 2
+            columns[3:] = conda_extra_columns
+        if pipver is not None and condaver is None:
+            source, version = "pip", pipver
+        elif pipver is None and condaver is not None:
+            source, version = "conda", condaver
+        else:
+            if (pipver == condaver):
+                source, version = "both", pipver
+            else:
+                source, version = '**CONFLICT**', f'pip={pipver}  conda={condaver}'
+        if 'CONFLICT' not in source:
+            version = '= ' + version
+        columns[1:3] = [source, version]
+        return columns
+
+    for key in package_names:
+        table.rows.append(version_summary(key,
+                                          pip_info=pip_info,
+                                          conda_info=conda_info))
+
+    # Pre-style the table output.
+    table.maxwidth = 9999
+    table.columns.alignment = bt.ALIGN_LEFT
+    table.set_style(bt.STYLE_COMPACT)
+    return table  # Ready to print
+
+
+if __name__ == '__main__':
+    env_info = scan_env()
+    table = make_package_table(*env_info)
+    print(str(table))