Having had the odd run in with dodgy clampers myself in the past this is a good thing. My solution* was to get myself a two foot long set of bolt croppers and "take care of business", even managed to return them to the supplier in "as new" condition for a refund after the job was done.

* I wouldn't reccomend it though, some of these blokes are nasty fuckers and, of course, if they do have the legal right to clamp you you'll only get yourself in a whole world of trouble.