I am in Essex , and the local 'sink' hole estate was having a social disturbance by these I'll mannered yoofs, ......and it's very true , that this was Essex police's response , just parked up a knackered old patrol car as a "'Police' presence, ..... It's lateral thinking, but like a rat trap, once sprung it doesn't work a 2nd time.
Another ploy to curb speeding is they will park a camera van up.on an over bridge ,it's in manned but occasionally lights are set off , as if a speed camera has been set of, whether or not that is legal I don't know, but they do need to be shown to be calibrated.