Just because the "gun" is pointing at every vehicle, it doesn't mean it's active - takes to long to raise the "gun" up and aim if they wait for the suspecion.

But the reality is that only those who commit an offence have anything to worry about.

Kind of off the point. Lets say I and every other vehicle had a detector registering a radar signal. Is that legal?

Perfectly legal in the UK to use a radar and laser detector. What is not legal is a laser jammer which interferes with the laser signal for a short period to give the driver time to slow down.

It sounds as if the speedwatch clowns have been given old radar guns to play with, the real police don't use radar guns any more, they pick up anything in the neighbourhood, such as cars driving the other direction away from the gun, flying birds, vibrating telephone wires, and nowadays also the green dreamer's windmills!