The British Rail Class 91 is a high-speed electric locomotive, which produces power of 4,830 kW (6,480 hp); it was ordered as a component of the East Coast Main Line modernisation and electrification programme of the late 1980s.

The Class 91s were given the auxiliary name of InterCity 225 to indicate their envisaged top speed of 225 km/h (140 mph); they were also referred to as Electras by British Rail during their development and throughout the electrification of the East Coast Main Line.

Unusually, the motors are body mounted and drive bogie-mounted gearboxes via cardan shafts; this reduces the unsprung mass and hence track wear at high speeds.

Its in-house forecasts determined that increases in revenue and considerable reductions in energy and maintenance costs would occur by electrifying the line.

Shortly thereafter, two alternative options were explored, an electrified version of the InterCity 125 (known as the HST-E), and the Class 89 mixed-traffic locomotive; these were both intended to a peak service speed of 125 mph.

[14] Some officials within British Rail pushed for more demanding requirements for the future Intercity trainset; reportedly, BR's Director of Mechanical and Electrical Engineering (M&EE) was a strong proponent for increasing the top speed to 140 mph.

While BR's board had approved the ordering of a single Class 89 as a prototype, the Strategy Committee queried why the type had been favoured over a proposed 80-tonne Bo-Bo locomotive.

[14] Appraisals also determined that the Class 89 was comparatively inferior in financial terms, in part due to the InterCity 225's prospective compatibility with WCML traction, reducing its development costs.

Despite this, the HST-E effort was promptly aborted, while Brush Traction decided to de-prioritise work on the Class 89 after learning that it was unlikely to lead to volume production.

[14] At one point, it was envisaged that the InterCity 225 would be extremely ubiquitous, even potentially having the capability built into it to operate over the southern third-rail network and within the Channel Tunnel; by mid 1984, such proposals were curtailed.

[14] A pre-qualification document was formalised, in which various requirements for the type were laid out; these included the need to perform mixed-traffic duties (day and night passenger, parcel and mail, and overnight heavy freight services), the haulage of both tilting and conventional rolling stock, a top speed of 225 km/h, a maximum cant deficiency of 9° without the provision of tilt equipment, and that the maximum unsprung mass could not exceed 1.8 tonnes.

[14] The prequalification document was issued to BREL, Brush Traction and the General Electric Company (GEC), as well as the French firm Alsthom and Germany's Krauss Maffei.

[14] The tendering process was relatively complex, but a decisive move appeared to have been GEC's offer of a sub-contracting arrangement to BREL for the construction of the locomotive's mechanical elements.

[9] In the early 1990s, after the cancellation of InterCity 250, British Rail examined the option of ordering a further set of ten Class 91s to operate on the West Coast Main Line with UK Treasury support, however the business case for these failed to prove sufficiently worthwhile.

[16] Eversholt put all 31 locomotives through a £30 million heavy overhaul and refit process (known as Project Delta[citation needed]) between 2000 and 2003, seeking to improve the fleet's reliability.

[16] The refit was performed by Adtranz (later Bombardier Transportation), with technical support from Alstom, and involved upgrades to the bogies, electrical systems, air compressors, and parking brakes; alterations to the cab layout at the Number 1 end; the replacement of the original gearboxes with newly designed Voith models; and the installation of TPWS and a new air-cooling system.

[18] In November 2012, number 91114 had a second pantograph added as a pilot project conducted jointly by Eversholt, East Coast, DB ESG, Wabtec, and Brecknell Willis.

If there is an ADD (Automatic Dropping Device) activation or the pantograph becomes detached, the train can keep going, so the system provides redundancy in the event of a pantograph/OLE failure.

[21] Locomotive 91012 (now 91112) holds the separate record for the fastest non-stop journey between London King's Cross and Edinburgh Waverley; 3 hours 29 minutes on 26 September 1991,[9][22] running within the 140 mph (230 km/h) speed limit but hauling a shortened set of only five coaches plus DVT.

[23] Regulations throughout Britain were subsequently amended to require the use of in-cab signalling whenever running service trains at speeds above 125 mph,[23][24] an option that BR were unwilling to pursue at the time.

National Express East Coast originally planned to repaint all of their InterCity 225 sets in the white and silver NXEC corporate livery within two years.

91109 as Sir Bobby Robson with cast-iron plates, unveiled in a ceremony at Newcastle station on 29 March by his widow Elsie and Alan Shearer.

Rail Operations Group have taken a pair of Class 91s for use in testing of the newly electrified Midland Main Line prior to the introduction of regular electric services between Bedford and Corby.