 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 , 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 Railway networks.