With a properly prepared case, its easy, clampers dont have a leg to stand on, legally. Go read the Pepipoo site, link above. The only reason hes got wealthy is because people are ignorant of there rights and the law, and pay up with a whimper and never bother challenging him.
I have a 800w petrol generator in the boot of my car for various reasons, and an angle grinder. If anyone dares clamp me on private land I shall exercise my legal right of self help from being illegally and wrongly clamped and cut it off. Then ill see the guy in court if he wants to make a fuss, and ill win, make no mistake, because im 110% sure of my legal rights from much advice from people who know, proven in real life cases.