Wheel clamping of bikes and cars.

I did a quick search on wheel clamping of bikes and cars and found nothing. As I understand anyone that is not a policeman/ traffic officer may clamp you vehicle whether it is at a shopping center, office park or blocks of flats. The reason for this is that should this person have an emergency and cannot use their vehicle and someone's life is in danger or in fact dies because of this they can be sued. The same applies to someone towing your car at the airport or in the city of not manned or operated by a policeman or traffic cop. Can anyone shed any light on this for me. We have seen many articles re non registered people getting summons's signed that is also illegal. We must have some seriaaas legal boffins that can help us all.