I have just received a windscreen PCN from one of the council parking enforcers - I know these you can't appeal
Err, you can always 'appeal'* a windscreen PCN.
*Or to be more accurate, one can always
make an informal challenge, and if that is unsuccessful,
make representations against the NtO (Notice to Owner) and if these are unsuccessful,
make an appeal to the Tribunal which may be successful.
Of course, some PCNs are issued correctly, and the Council has a watertight case,
but you would be surprised at how often the Council makes a mistake, either in interpreting the relevant legislation or in the 'small print' of the PCN, which leads to cancellation of a PCN.