You're right, I don't remember any cameras on the M25. However, I do remember cameras on the M40 going to Birmingham. We were doing 90 on the outside (or inside depending on how you look at it) with a copper on a motorcycle behind me. I thought that he would "blue light" me, however, all he wanted to do was pass. It seems that in the UK & Europe reckless driving is more important to ticket than speeding. Cheers!