The classes 310 and 312 were electric multiple units designed for the 25.000 Volt AC network and based on the body of the Mark 2 coaches. They had a huge number of slam doors to ensure rapid entering and exiting of passengers. They originally consisted of four cars of which one of the inner ones was powered on all four axles with 270 kW each. Since the powered car also contained the pantograph, transformer and rectifier, it was more than 20 tons heavier than the other ones.

50 sets of the class 310 were built between 1965 and 1967 as part of the electrification of the West Coast Main Line. It was originally called AM10 and had a top speed of 75 mph (121 km/h). It was the first mass-produced multiple unit in Britain with disc brakes and had a glass wall behind the cab, allowing passengers to view the line. Thirteen sets were converted to three cars and called class 310/1.

Of the class 312, 49 sets were built between 1975 and 1978 for lines to the east and north east of London. These were faster at 90 mph (145 km/h) and were more modern in many details. Some were also equipped for a voltage of 6,250 used on some lines to the east and north east of London and were designated class 312/1. In the eighties they were superseded by new EMUs with a top speed of 100 mph. After being refurbished and being used for other services, most sets of the classes 310 and 312 were withdrawn between 2001 and 2004.