We had an unmarked Renault pull in front of us going through Tours, it seemed strange as it had come up fast to overtake us, I then noticed the camera in the back and so was on my guard but I was OK for the speed limit, It then braked and immediately zoomed off only to come back again to repeat the move. I slowed down very quickly and made sure I had a couple of cars between us, it then zoomed off up the road. I don't know if it could get a false speed reading from doing this but took no chances. Not had any fine and its 12 months plus now.