I've been stopped by the police a few times for traffic violations. The first time was when I was a kid, and I was cycling home after dark without lights (I'd got lost, so I wasn't expecting to be out that late). The policeman who stopped me let me store my bike in his shed overnight, then I went back the next day to pick it up.
The second time was when I was moving house, and I was driving through London at about 3am in a rented transit van. The streets were pretty much deserted, and my mind was wandering slightly, when I suddenly realised that the traffic light ahead of me was red. I could have done an emergency stop, but I thought "the only other vehicle around is a car that's up a side road, and it's stationary, so there's no danger of me hitting anyone if I just go straight through". As I went past the traffic light, I noticed that the parked car was actually a police car (d'oh!). Anyway, the car followed me, and flashed lights for me to pull over. We both stopped, and got out of the respective vehicles. He asked me what colour the traffic light was, and I admitted that it was red, and apologised. Then he asked me whether this was my own vehicle, and I said no, gesturing at the big sign on the side of the van that said "Hertz rent-a-car" (or something similar), but I made an effort not to sound sarcastic. The point is, I made an effort to be polite, I admitted what I'd done, and I accepted full responsibility for it - I made no attempt to justify my actions. So, he let me off with a warning. The thing is, it's not a trick, just close to a paradox; if he'd arrested me, or put points on my licence or something, then I would have accepted that. I wasn't just saying it to get out of trouble. But because I was willing to take the blame, I didn't need to. By contrast, if I'd taken the attitude of "Come on, nobody's around, so who cares? Why aren't you out catching real criminals?" then I don't think it would have gone as smoothly.
The third occasion was when I was on my motorbike, coming home to Hooper Street. As you can see from the map (if you follow that link), there's a one-way system around there. If you're travelling north along Dock Street (which becomes Leman Street), you aren't allowed to turn right into Hooper Street. Instead, you need to go "round the block", by turning left into Prescot Street, then right into Mansell Street, right into Alie Street, right into Leman Street, then left into Hooper Street when you get back to the point where you were initially. I would normally go round the long way, to follow the rules, but lots of other people didn't. So, there was one evening when I was coming home, and I just thought "Why should I be the only one who does it the right way, if everyone else is cutting the corner?", so I turned right into Hooper Street. It then turned out that there was a police car behind me, who pulled me over. They asked whether I'd seen them, which put me in a rather awkward situation - if I said "yes", then that meant "I knew you were there, but decided to blatantly break the law in front of you", which is bad. If I said "no", then that meant "I didn't check my mirrors properly before I made the turn", which is also bad. So, partly since I was in trouble either way, and partly because I don't like to lie, I opted for the truth, which was to say "no". In my defence, I knew that there was a car behind me, I just hadn't looked closely at its markings, although again I didn't spell that out to them. Anyway, I think it helped that I had L-plates on my bike at that point, as they asked me how long I'd been riding a bike for, and I said "a few months" which was true. I offered to show them my driving licence, but they said that if they'd wanted to see it then they would already have asked me for it. Mind you, if they had seen it, they would have noticed that although I was a learner motorbike rider, I'd passed my car test five years previously. I don't know whether that would have made a difference. Anyway, a similar thing applied - I readily admitted that I knew it was wrong, and had done it anyway, and I apologised for it, and they let me off with a warning. Which worked, since I never did it again.
The only other situation which sort of counts occurred last summer. That's kind of a grey area, since I'd stopped to help the police, rather than them stopping me, so I think it was a case of the police officer turning a blind eye.
So, that's my sordid criminal past exposed :)