Best thing was though the plum copper forgot to record the speed he was doing so they had to let him off (after he asked for proof which they couldn't give him) 
I saw an interview with a US cop who said the first thing they ask you when they pull you over is how fast you were going (as we all know). He said they do this because most people, knowing they were doing 40 in that 30, say something like 33 or 34 thinking it looks better to admit to a small infraction. This is basically a confession to breaking the law and takes no admin on the old bill's part. He said never admit to anything, they often don't have proof or its just too much work for them. The whole lecture was fascinating stuff actually, you tube has it under "don't talk to the police" or something like that.
That said, antagonising the fuzz might land you the maximum penalty, so denying something they obviously got you on is probably not the best strategy if you want to get away with a fine and no points for example. I guess you gotta play it by ear. From watching a episodes of traffic cops it seems you can get anything from an ok bloke to one who is gonna pull you over on a whim and then go over your motor with a fine toothed comb just to get you on something.
And as usual I've gone waaay off topic.
