British Rail Class 317

The BR Class 317 was a fleet of seventy-two four-car 25 kV AC electric multiple unit sets built at BREL York between 1981 and 1987, designed for outer-suburban services on the electrified routes out of London King’s Cross and London St Pancras. The class was one of the most significant EMU designs of the 1980s, providing a substantial improvement in comfort, speed, and capacity over the first-generation suburban EMUs it replaced and establishing the BREL York outer-suburban body design that would influence subsequent classes including the Class 319, 321, and 322.

The Class 317 was originally ordered for two specific electrification schemes: the Bedford–St Pancras Midland City Line electrification at 25 kV AC, which opened in 1983 and for which the first Class 317/1 sets were built; and the Great Northern outer-suburban electrification from King’s Cross to Peterborough and Cambridge, which was completed in 1987–88 and required the second batch of Class 317/2 sets. The two subclasses were mechanically identical but built to slightly different specifications reflecting the different route characteristics and passenger markets — the Midland City sets had a higher proportion of first-class seating for the Bedford commuter market, while the Great Northern sets were configured for the heavier, longer-distance flows to Peterborough and Cambridge.

Each four-car set consisted of a Driving Motor Brake Standard, two Trailer Standards, and a Driving Trailer Composite, with a total power output of approximately 1,600 hp from the Class 317/1's thyristor-controlled traction system. The maximum speed was 100 mph, significantly faster than the 90 mph Class 310 and 312 sets and appropriate for the semi-fast and express-stopping services the class was designed to work. The interior offered a considerable step forward in comfort, with better seating, improved soundproofing, and air conditioning on the later 317/2 sets.

Under privatisation the Class 317 fleet was distributed among Thameslink, First Capital Connect, and Greater Anglia. The Thameslink sets worked the Bedford–Brighton and Sutton–Luton cross-London services through the Thameslink route; the Great Northern sets worked King’s Cross outer-suburban services to Cambridge and Peterborough. Greater Anglia operated a small allocation on Stansted Express and West Anglia services. The last Class 317s in regular service were retired by Greater Anglia in 2022, ending a forty-year career. Several sets have been preserved, including examples at the Ecclesbourne Valley Railway and by private groups, making the Class 317 one of the few BR EMU classes to have entered heritage preservation.