Wheel clamping on private land has been illegal in Scotland since 1992 when Scottish courts ruled that it amounted to extortion. Motorists in England have no such protection and have no independent appeals body to refer to if they've been overcharged or have been conned by a private car firm.
Clamping can be such a lucrative business for firms that many charge landowners nothing for parking enforcement, receiving all their income from the cars they clamp, giving them little incentive to deter parking.
The Government have begun a consultation into clamping but have ignored the option to ban clamping on private land entirely. To have your say, visit the consultation website http://www.homeoffice.gov.uk/documents/cons-2009-vehicle-immobilisation/.