`cf.read` fails on `.pp` files

[woutersj]

I have .pp files from FAMOUS, based on UM 4.5, that don't read in newer versions of cf. They read fine in versions 3.16.3 and 3.17.0, but not the more recent 3.18.0 or 3.18.1.

I have uploaded an example file here

The error is

>>> cf.read(fname)
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    cf.read(fname)
    ~~~~~~~^^^^^^^
  File "/home/jeroen/Projects/famous-amoc/venv/lib64/python3.13/site-packages/cfdm/decorators.py", line 171, in verbose_override_wrapper
    return method_with_verbose_kwarg(*args, **kwargs)
  File "/home/jeroen/Projects/famous-amoc/venv/lib64/python3.13/site-packages/cf/read_write/read.py", line 528, in __new__
    return super().__new__(**kwargs)
           ~~~~~~~~~~~~~~~^^^^^^^^^^
  File "/home/jeroen/Projects/famous-amoc/venv/lib64/python3.13/site-packages/cfdm/decorators.py", line 171, in verbose_override_wrapper
    return method_with_verbose_kwarg(*args, **kwargs)
  File "/home/jeroen/Projects/famous-amoc/venv/lib64/python3.13/site-packages/cfdm/read_write/read.py", line 282, in __new__
    for dataset in self._datasets():
                   ~~~~~~~~~~~~~~^^
  File "/home/jeroen/Projects/famous-amoc/venv/lib64/python3.13/site-packages/cfdm/read_write/read.py", line 400, in _datasets
    raise FileNotFoundError(
        f"No datasets found from datasets={kwargs['datasets']!r}"
    )
FileNotFoundError: No datasets found from datasets='/home/jeroen/um/um_archive/xpnib/xpnibo#pg000000023c1+.pp'

Output of cf.environment(paths=False)

Platform: Linux-6.15.9-201.fc42.x86_64-x86_64-with-glibc2.41
Python: 3.13.7
packaging: 25.0
numpy: 2.3.2
cfdm.core: 1.12.3.0
udunits2 library: libudunits2.so.0
HDF5 library: 1.14.2
netcdf library: 4.9.4-development
netCDF4: 1.7.2
h5netcdf: 1.6.4
h5py: 3.14.0
zarr: 3.1.2
s3fs: 2025.7.0
scipy: 1.16.1
dask: 2025.7.0
distributed: 2025.7.0
cftime: 1.6.4.post1
cfunits: 3.3.7
cfdm: 1.12.3.0
esmpy/ESMF: not available
psutil: 7.0.0
matplotlib: not available
cfplot: not available
cf: 3.18.1