British Rail Class 312

The BR Class 312 was a fleet of forty-nine four-car 25 kV AC electric multiple unit sets built at BREL York between 1975 and 1978, produced as a development of the Class 310 for outer-suburban services on the Great Eastern main line out of London Liverpool Street and on the West Coast Main Line. The class represented a second generation of WCML and Great Eastern suburban EMU, incorporating improvements over the original Class 310 fleet while maintaining the basic four-car mixed-class formation appropriate for outer-suburban operation.

The Class 312 was designed around the same 25 kV 50 Hz overhead supply as the Class 310 but with updated electrical equipment and a revised interior specification. Each set consisted of a Driving Motor Brake Standard, two Trailer Standards, and a Driving Trailer Composite — the same mixed first and standard class configuration as the Class 310 — with a maximum speed of 100 mph, slightly higher than the Class 310's 90 mph limit. The BREL York body was a development of the standard BR Mk 2 suburban EMU profile, clean and functional if not distinguished.

The Class 312 fleet was split between two operational areas: the majority were allocated to the Eastern Region for Great Eastern outer-suburban services from Liverpool Street to Clacton, Southend Victoria, and Cambridge, where they replaced ageing first-generation EMUs and locomotive-hauled coaching stock; a smaller allocation worked WCML outer-suburban services from Euston to Bletchley and Northampton. The Great Eastern allocation gave the class its most prominent work — the busy outer-suburban flows of the Essex and Hertfordshire commuter belt — and the 312s became a familiar presence on Liverpool Street arrivals and departures through the late 1970s, 1980s, and into the 1990s.

Network SouthEast inherited the Class 312 fleet in 1986 and rebranded the sets in NSE colours. Withdrawal began in 1995 as the Class 321 arrived on Great Eastern services, and the last examples were retired in 2003–04. None was preserved, making the Class 312 another gap in the preservation of Britain's electric multiple unit heritage.