Between 1981 and 1996, British Railways received a large number of electric multiple units based on the Mark III coach profile. Unlike some previous units using an aluminum body, they were all-steel. With a total of two to five cars per set, all classes have one car with four traction motors of different power. The classes 317 to 322 are four- or five-car sets for 25 kV AC with a top speed of 90 or 100 mph.
The class 325 is similar to the classes 317 to 322, but has no seats, no windows and is being used by the Royal Mail. The classes in the 400 range designate EMUs for service under DC with third rail. While the class 442 consists of five cars and reaches 100 mph, the classes 455 and 456 consist of four and two cars and are being used for suburban service with a top speed of 75 mph.
Apart from the electric units, only two prototypes of the class 210 were built with diesel-electric propulsion. In the end these were not built in series, since other DMUs with hydraulic transmission were ordered. Most trains of the electric variants are still running. Many were refurbished in the first 20 years of the 21st century.