Until you do the above 3 times and whoops, time to re-take your test...
I speed as much as the next person (well, every now and then) and I've always thought it was daft that we could see the cameras, as all that does is make me brake just before it, trundle through at the correct speed, then zip off afterwards.
You can all argue until your face turns blue about how unfair the law is, but let's face it, you know you're breaking it and (in most cases) getting away with breaking it day in, day out.
If we can't see cameras, or don't know their whereabouts, we will be slower all the time, for fear of losing money/licence. That's the effect cameras should have. Not the panic-braking of the car in front of you who wasn't watching and nearly caused an accident as you just managed to avoid rear-ending him/her.