Speed camera on the M5

While driving up the M5 (North) today I noticed on my Mitac MIO168 GPS PDA running tomtom 3, with speed camera support, just before the M42 junction, a camera sign the screen of the PDA, sure enough on the last bridge before the brow of the hill on each lane were what looked like speed cameras, I did slow down but most over cars seemed to be wizzin though at 80 plus, my question is:

1. are these functioning?
2. should there not be a warning sign of there presence at least a mile before?

regards

Wayne

Landy V8 hybrid RR 4.0SE