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| Class 31 | |
|---|---|
| Name | Class 31 |
| Powertype | Diesel-electric |
| Builder | English Electric |
| Builddate | 1957–1962 |
| Totalproduction | 263 |
| Primemover | English Electric 16SVT |
| Transmission | DC generator, DC traction motors |
| Wheelarrangement | A1A-A1A |
| Gauge | Standard gauge |
| Locoweight | 106–117 t |
| Topspeed | 80 mph (129 km/h) |
| Poweroutput | 1,470 hp (1,100 kW) |
| Tractiveeffort | 41,000 lbf |
Class 31 is a type of British diesel-electric locomotive introduced in the late 1950s by English Electric for the British Railways Modernisation Plan. Designed for mixed-traffic duties, it served across many regions on the InterCity network, secondary routes, and freight services, later appearing in preservation and film. The class influenced subsequent designs and underwent multiple rebuilds and reclassifications during its career.
The design originated from English Electric at Newton-le-Willows and Vulcan Foundry workshops under pressure from the Modernisation Plan (British Railways), drawing on experience from the Deltic and Class 20 programs. Initial prototypes were trialed on routes serving London King's Cross, Crewe, Carlisle, Edinburgh Waverley and Birmingham New Street to validate the 16SVT prime mover and A1A-A1A axle arrangement. Early meetings with British Transport Commission engineers, Robert Riddles advisors, and Doncaster Works staff shaped weight distribution, cooling systems, and driver visibility. The class' external styling reflected contemporary trends set by British Railways design teams and the influence of English Electric orders for South African Railways and Commonwealth Railways.
Powered by the English Electric 16SVT four-stroke V16 diesel installed with a DC generator and English Electric traction motors similar to those used on Class 37 prototypes, the locomotive had a continuous output of about 1,470 hp. The A1A-A1A wheel arrangement reduced axle load for secondary routes serving Scotland and the Western Region, enabling operation over lighter track at depots such as Stirling and Worcester. Braking systems followed BR vacuum and later dual braking conversions compatible with Mark 1 coaching stock and Freightliner wagons. Electrical auxiliaries and multiple-working equipment were standardized to interface with Blue Star and other compatibility systems used across British Railways.
Introduced in 1957, the class rapidly replaced steam locomotives on secondary express and freight workings, appearing on diagrams from Paddington out to Penzance, and northbound services to Glasgow Central via Carlisle. Units were deployed by Eastern Region, London Midland Region, Western Region and Scottish Region sheds including Doncaster, Heaton, Tinsley and Crewe South. During the 1960s and 1970s they hauled named trains, freight turns to Felixstowe and Dover, and relief diagrams during events at Wembley Stadium and Edinburgh Festival. Several were withdrawn or stored following The Reshaping of British Railways rationalizations, while others found new life with sectorisation under Regional Railways and Railfreight.
Allocation patterns shifted with traffic demands: many units were concentrated in the North East and Scotland for secondary expresses and parcels traffic, while a cadre served South Wales freight and cross-country diagrams. Depot allocations evolved through reshuffles at Longsight, Heathrow, St Rollox and Laira as InterCity dieselization and electric electrification projects altered route workings. The class saw mixed-traffic duties including passenger diagrams with Mark 2 coaching and locomotive-hauled parcels for Royal Mail traffic. Leasing and departmental transfers later placed examples with Network Rail contractors and private operators such as EWS and Direct Rail Services.
Substantial rebuilds produced sub-classes with different features: repairs and re-engining trials introduced higher-rated engines and improved cooling borrowed from Class 37 designs; headcode and marker light reconfigurations aligned units with TOPS numbering introduced in the 1970s. Some locomotives were converted to carry electric train heating or fitted with dual-brake appliances to work with Mk 3 or Mark 1 stock. Departmental conversions included sandite and route-proving units for British Rail Research and infrastructure contractors. Experimental modifications tested turbocharging and altered gearing for freight duties serving depots like Dagenham and Immingham.
Throughout their career, a number of units were involved in derailments, collisions and fires on main lines near Crewe North, Swansea and York, often reported alongside investigations by the Railway Inspectorate and operational follow-ups by British Transport Commission successors. Notable incidents prompted technical audits and brake system upgrades, with some damaged examples cut up at works in Charlesworth or Doncaster. Investigations occasionally led to procedural changes at signal boxes like Ganister and alterations to routes used for heavy freight flows to ports such as Liverpool and Immingham.
A selection of locomotives was rescued by heritage railways and preservation groups including North Yorkshire Moors Railway, Keighley and Worth Valley Railway and Spa Valley Railway, appearing alongside preserved stock from British Railways eras. Preserved examples have operated on galas at Severn Valley Railway and heritage tours to Bath and York, maintained by volunteers from societies modeled on the National Railway Museum conservation practices. Museums and trusts have displayed units in running condition and static exhibits, occasionally loaning locomotives to events such as the Railway Heritage Festival.
Locomotives of the type featured in television programs, documentaries and films shot around London, Yorkshire and Scotland, appearing in dramas set during the postwar period and modern reenactments for series filmed by companies like BBC Television and ITV Studios. Photographers and authors from publications tied to Platform 5 and Ian Allan Publishing documented the class extensively; enthusiasts congregated at photo-stops near Didcot and Matlock for laden freight and express rehearsals. Models and kits were produced by manufacturers such as Hornby, Bachmann, Dapol and Lima, cementing the locomotive’s presence in railway modelling circles and transport history exhibitions at institutions including Science Museum and Locomotion.
Category:British diesel-electric locomotives