This may help, particularly if it is a private parking company
http://forums.pepipoo.com/index.php?autocom=ibwiki&cmd=article&id=56
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PRIVATE PARKING COMPANIES RELY ON THE LAW OF CONTRACT
And while contract law can be a minefield of offer, acceptance, terms, implied terms and clauses, it can be surprisingly easy to understand in terms of every day matters such as this.
Essentially when a driver of a vehicle drives into a car park and parks his car he is implied to accept the offer for parking on the terms of the offeror (the parking company or land owner). A contract is formed and therefore the contract can be broken (or breached).
The Private Parking Company (PPC) must make the terms clear to the user of the car park. Therefore they are obliged to place ample and appropriate signage about the car park to make those persons using the facilities aware of the terms. The signs must be clear and unambiguous and it cannot be obscured, faded, covered up or in any way difficult or impossible to read and understand. Often times those terms will include a provision that if you over stay you will be penalised to the tune of £50, £70 or whatever. They may also include a clause on clamping (I will not be dealing with the issue of clamping in this article). These signs are usually displayed at the pay stations (for pay and display) and for other car parks at the entrance and at intervals about the land. If the car park is improperly signed then immediately the PPC will be in difficulty. Thus when the driver parks the vehicle in the car park and pays or otherwise he accepts by way of his actions and a contract is formed between he and the owner of the land.
ONLY THE DRIVER AND THE OWNER OF THE LAND ARE A PARTY TO THE CONTRACT UNLESS THE PARKING COMPANY ACTS AS THEIR AGENT