Ok, so it was my mistake. I had a parking permit for the apartment block but was distracted by my young son and so stupidly left the permit in the door pocket of our Discovery. Predictably I came back to find a sticker on the window and a clamp on the wheel.
Worse was that the clamper was still in attendance - from the ironically named Ace security of London - filling up the underground car park with fumes from his van which he hadn't bothered to switch off.
I thought it was worth protesting and even showed him the undisplayed permit. It didn't cut any ice though - he mumbled "I've already logged it and taken the pictures, mate." I could also appeal but only after I'd paid up and I didn't really need to imagine how futile that may be...
So how much to remove the clamp so I could use my car again? £120. That's right, 120 quid!!
Just to recap, these clampers can charge three times the cost of a parking ticket - and more to the point charge what they like.