If its a mobile camera, they dont even bother stopping you, Just send you a letter through the post.
Correct, remember there are basically 3 types
1. Permanent fixed point which only takes a photo if going over the actual speed for that spot and can't tell if it's a car, van, lorry or plane.
2. Mobile camera units which have to be marked up as such, but it's manned by a human (so to speak) and the guy operating it can tell the difference between car, van, lorry and can submit the evidence as such. Some radio ahead so you get stopped some distance ahead or they take the pictures back for processing.
3. The unmarked stealth patrol who have to follow for one quarter of a mile in order to get enough evidence, hence some of those large white blobs of white paint on some roads, and then pull you over
At least with No 3 you'll be more inclined to stick to the speed limits for a while after the offence, unlike No 1 and to a degree No 2 which doesn't do anything to slow you down on the day but just rings the cash till.