They're not a scam. Owners of car parks are empowered to make excess parking charges under the Road Traffic Act 1984, in exactly the same way that local authorities are. The reason that failure to pay seldom results in prosecution is because of the costs involved in court action.

BTW, anyone can get owner details from the DVLA. That's what you do if a car bashes into you and you aren't able to collect the owner's name and address or his insurance company.

Finally, it's not the driver who gets the charge but the vehicle's owner. Therefore, there's no need for proof as to who was driving it at the the time.

The best way to avoid excess parking charges is not to outstay your welcome.