This is not hearsay and supposition by the way, this is legal fact that has been tested many times in the courts, and as such most Supermarkets/private companies will not even bother to take you to small claims as they know the chance of them winning is tiny. They will just try to force you to pay using bluff and bluster. If you let the company know that you are aware they can only claim for loss of revenue, then that will be enough to make them halt. How many companies do you think would take you through small claims for the possible chance of £1 ?
The supermarket concerned put a representative up on Radio 5 last night and was asked if they had a legal right to issue fines - they claimed that all their supermarkets were managed by a car parking company ( name escapes me) , registered at the DVLA (?) and yes they were legally allowed to issue fines .
Does your information still apply ?