Thanks Saint V8! I have done all of the above checks. The only issues appear to be a problem with the parking sensors, which may be the module, or the individual sensors themselves.
I know of the owner who has had the car since 2004. He has four cars and doesn't need a large vehicle anymore. The car has always been garaged, and the rear seats have only been used a handful of times. The previous owner is also not short of a bob or two, and I know that any essential maintenance/repairs would have been carried out.
How is your V8 treating you, gathered you havn't had it long?