I borrowed this from another website forum I use, re people getting tickets, and th scamming firm "buying" the info off the DVLA.
"On private property that isn't controlled by a local authority, they cannot legally issue any kind of fine or penalty for a parking offence.
The so-called 'fine' they give you is actually a payment they ask for in return for not taking you to court for either civil trespass, in cases where parking is free and signs are displayed stating the time limit, or for breach of contract if they issued a ticket on the way in. Unfortunately, most people don't know the law and pay up without question.
Funny that the ticket you get on the windscreen or through the post looks a lot like a Police ticket complete with black and white checks though...
In the majority of cases where tickets aren't issued on entry and parking is free, these companies will never go to court if you refuse to pay. The reason is that the courts will almost always reject the company's argument that, by parking on the property you were accepting the terms displayed on the sign. This is considered a 'passive' contract and the courts usually throw them out.
Ticketed parking is more tricky legally because it's easier to argue that you actively accepted the terms of the contract. The companies still rarely pursue the non payers to court because it's too expensive to chase after the few that won't pay when most people can be scared into paying up for the price of a first class stamp.
If you get one of these - write to the Managing Director and ask him on what legal basis they feel that they can issue the penalty? Nothing frightens them more than a punter who knows the law!
I used to fight these all the time for people in my previous job and after 100's of threats I never had one go to court."
Just a modern da yequivalent of clamping