The British Rail Class 312 alternating current (AC) electric multiple units (EMUs) were built between 1975 and 1978 for use on outer-suburban passenger services. It was the last class of multiple unit to be constructed with the British Rail Mark 2 bodyshell, as well as the last class of multiple unit to be built with slam doors in Britain. These features contributed to their relatively early withdrawal at 25–28 years old, compared with a typical EMU life expectancy of 30–40 years.

These units were based on the Class 310 used on the suburban services out of London Euston but were rated for a top speed of 90 mph (140 km/h), and they had flat windscreens from the outset. The only significant difference between sub-classes was that the 312/1 units were also equipped to work on the 6.25 kV AC overhead electrification system used on parts of the Great Eastern Main Line and London, Tilbury and Southend line networks.

Vehicles 78037 and 71205 from unit 312792 have been preserved