Agreed, there is lots of misinformation on the web but pepipoo appears to be the best, much better than CAG or MSE for example.
Without seeing pictures of the signs dissplayed at the car park or indeed a sight of the parking charge notice itself, it is difficult to give a definitive answer, hence my use of the word 'usual'. If taken to court then defense rests on the fact that only a court can impose a 'fine'. A defense to a breach of contract will llimit the claimant to their actual loss, which for a car parking space would be�0.00