They do this a lot in South Wales (M4). They use a combination of speed and ANPR cameras.
We used to get a lot of tickets through the garage I used to work as the M4 would be used to test vehicles that were ready to go out to customers to ensure there was no noise/vibration at speed.
Regular appearances of these over the M25 around the Denham to Maple Cross section, they have one van, two men and 4 cameras that they position over each lane and they are there for six hours at a time.