Yes the camera's don't have to visible any more. The money raised by cameras used to be collected by the force but they took that away from them and relaxed the rules around how visible the camera needs to be so a hidden camera is just about catching people breaking the law. I think they can still claim money from the yellow boxes but not from things like this.
The only speed camera I operate has a smiley face on it unless you go over either 20 or 30 mph (dependant on the setting), for around schools etc...
