Not sure how I missed this post but a very similair thing happend to me last september.
I was visiting a site in Hayes and the only parking is a private car park, all the contractors have to use it unfortunately. Anyway I parked up and then realised that I didn't have any change for the bloke in the hut, no machines just an old git in a hut and he writes you a ticket.
I offered him a £20 note to which he laughed and said he didn't have enough change, no problem I said I'll get one of the blokes from the site to pop over with the change, the site is a stones throw away.
I rang one of my chaps and he came over with some change and we got the ticket and walked back to my car. It was then that we saw the clamp on the car. Whilst I had been waiting for my chap to come over with the change, about 3 mins, some other little sh** had clamped me.
We went back to the bloke in the hut and explained the problem and he just kept repeating that the clamp had gone on at 11.46 and my ticket had 11.50 written on it. The chap who bought me the change said that all the blokes on the site saw me drive in and that if it went to court he wouldn't have a leg to stand on. He just repeated the time on the ticket and the time it was clamped.
No problem I said as I rang another bloke to bring over a nice large battery operated grinder.
Five minutes later the clamp was in pieces with 3 monkeys standing round me wanting to kill me but not bothering as they were surounded by 15 hefty looking builders and electricians just waiting to pounce.
Needless to say I never recieved a court summons for criminal damage but I did have to find somewhere else to park whenever there was a site meeting at that particular job.
Sometimes it's best to play dirty and as I pointed out to them rather smugley as I drove off, they would now loose over £200 a week as my contactors would be banned from using their crappy parking facilities again.