The question of the status of �private� car parks arises quite frequently in these columns and it may help you understand the law. It came up a few days ago in another motoring question so I have reproduced part of the answer I offered then.
The various Road Traffic Acts (and, in some cases, the restrictions on cover provided by insurers) makes reference to �public� roads.
The definition of �public� is wide and has been tested many times in court. Essentially if the public has unfettered access to the area (even if that access is restricted at certain times because, say, the establishment it serves is closed) then it is considered a public road. This means that car parks serving shops and pubs, as well as municipal car parks operated by or on behalf of local councils are all public roads for the purposes of motoring law. It makes no difference who paid for their construction or who pays to maintain them. Beyond the law (or possibly arguably beyond the law) are private car parks such as those serving office blocks, to which only selected drivers have access.