Clampers dont have to be licenced do they?

Get a clamp from Halfords, Go down the car park and put up a small sign saying any vans in the car park will be clamped, Then next time they go down to Rip people off clamp thier van and charge em £300 to release it.... then if they remove the clamp or kick off get the Cops down again and say you want em done for criminal damage