Here is a great little film by Rajesh Thind documenting the growing camera paranoia here in the UK. It's interesting to note how the Police Community Support Officers (PCSO) back off when they realise they are dealing with someone who knows the law better than they seem to do.
I've never been stopped by the Police, maybe due to the large pro Nikon cameras i carry, but i was once stopped by a guy who thought i'd photographed his car. A car screeched up to the side of me and out popped two men. Both started firing off questions and during their outburst of accusations, it turned out that one of them had had a previous vehicle stolen recently and obviously thought that i was photographing his new one so that that could be stolen too. A student ID card proved to him who i was but if he'd have pushed further i would have taken it down to the local police station. Both men were reacting to me due to their own paranoia - just like the PCSO's in the film did to Rajesh's presence.
The car wasn't in any photo and i had a 200mm lens on the camera at the time. If i had tried to photograph his car, all i'd have got was a closeup of his Vauxhall badge!