The British Rail Class 312 alternating current (AC) electric multiple units (EMUs) were built between 1975 and 1978[7] for use on outer-suburban passenger services.

The design of these units was based on the Class 310 used on the suburban services out of London Euston, but were rated for a higher top speed of 90 mph (140 km/h) and they had flat windscreens from the outset.

As built, the 312/0 fleet were used on the newly electrified Great Northern outer suburban services from London King's Cross to Royston.

These were used mainly on Colchester to Walton-on-the-Naze and Manningtree to Harwich services and London Liverpool Street to Ipswich and Clacton peak trains.

The final sets were used on peak trains and were withdrawn on 25 June 2004 after the return of the five Class 322 units, which had been on hire to ScotRail.

[9] Following the closure of the ERM, both vehicles moved to the Colne Valley Railway, Essex in March 2018, taking them back to their native operating area.