Neil unfortunately has it wrong wrt the Parking Eye situation.
If Parking Eye were to try to enforce these 'invoices' (not legally parking fines), they would need to prove the following:-
1. Who was driving. Any 'invoice' would need to be sent to the driver, not the vehicle!
2. That the 'invoice' reflected reasonable compensation for the damage inflicted on the business - in a civil court a penalty over and above reasonable compensation would not be entertained (see the level of the 'charge' itself, the £30 'admin fee', the £2.50 'charge' for using a debit card to pay over the internet).
3. Other areas related to the actual existence of a legal contract in the first place - check out http://forums.pepipoo.com/index.php?showtopic=46975
for further details, or go on YouTube and see an expert solicitor giving advice on what to do with such 'invoices' on Watchdog (it involves making a paper plane).
There is a very good reason why Parking Eye have never taken anyone to court - they wouldn't have a hope in hell of prevailing and this action would set a rather unfortunate precedent in terms of the viability of their 'business' model.
It doesn't suprise me that private parking companies moved on from one scam (clamping) to another (ticketing with ridiculous 'charges', deliberately mimicking the design of official legally enforceable penalty notices). What does suprise me is that Welcome Break would risk reputation by using their services, without paying any particular notice to the 'charge' structure.