Hi all, the below was published by the times on 31st October so hopefully it hasn't changed since then;
Alternatively, you can be pulled over by a police officer. To pull you over and report you, a police officer will have to have evidence of your speed. They can obtain this either by using a speed gun, or through the use of a camera car or bike. (NB: on a motorway, the officer does not need any extra evidence of speeding. The officer's opinion is enough to prosecute.)
A speed gun is a hand-held radar device that officers point at an oncoming car, to provide them with a readout of its speed. Often, one officer will use the speed gun, while another waits further down the road; the first officer then radios ahead a description of the speeding car to the second, who then pulls that car over.
Alternatively, officers who spot a speeding car while out on the road can follow the car and pull it over. While they’re following the car, an in-car camera system can give them a read-out of its speed, and records footage of the car to use as evidence. The officer then uses blue flashing lights to pull the car over, and will deal with the driver in person, usually in the back of the police car.