The unmarked cars camouflage themselves by parking on the hard shoulder with hazard lights on and just look like an ordinary break down while using their rearward looking radar/laser to catch speeders.
So they will get hit up the ar$e by a sleepy trucker like the rest of the people sitting idle on the hard shoulder then.
They must of ran out of those 'sidings' ...."For Police Vehicles Only" which tend to be most noticeable on the M5....
On the A361 near Tiverton, the police vehicle hides behind the hedge and the officer pokes his little rays out the hedge...then radios to another traffic vehicle waiting a mile up the road...!
Razor