In 1900 the British Westinghouse Electrical & Manufacturing Co Ltd bought land in Trafford Park and built a factory which went into production in 1902 for the manufacture of mechanical and electrical equipment for the generation, transmission and use of electricity. In 1919, Trafford Park Works became owned by British Westinghouse’s successor, Metropolitan-Vickers Electrical Company (MV). The main shops, in common with factory construction throughout Trafford Park, were single floor type, with bays 1,000 feet in length, and had direct railway communication with the docks and trunk systems of the country. The main office block was a copy of the Westinghouse building in Pittsburgh, USA and the factory was to the American design and used imported steelwork for construction. Products manufactured at the Works included gas engines, stationary steam engines, electric generators, transformers, switchgear, meters, motors, control gear, and arc lamps. During the First World War, British Westinghouse built some small petrol-electric locomotives for the War Department Light Railways. In 1928 the Works were taken over by Associated Electrical Industries (AEI), which merged Metropolitan-Vickers and British Thomson-Houston, though these two companies continued their own trading names. Traction design and manufacture was always a minority of the workload at Trafford Park with the largest operations generally turbine manufacture. Very few vehicles were built there, and traction machines (i.e. motors, inductors and generators) were largely built in other places – notably at Sheffield or Rugby. Trafford Park traction manufacture was largely that of assembling control gear – contactors, switches, drivers’ controllers, camshaft controllers, relays etc. and building these into frames or equipment boxes for installation in vehicles made elsewhere. An important part of the Trafford Park Works site was the general switchgear operation, mainly for generation or distribution installations. The on-site Switchgear Testing Company was a “testing house” for these products and contributed to testing and development of traction circuit breakers and switchgear. During the Second World War MV acting for the Ministry of Aircraft Production produced more than a thousand Lancaster Bombers in the adjacent Mosley Road building. The company also manufactured war munitions and in the laboratories developed what became known as Radar. In 1959 the newly formed AEI Traction Division established its headquarters at Trafford Park, with a product range that included electric and diesel-electric locomotives; electrical equipment for tram-cars, trolley buses and trolley mining locomotives and traction motors. AEI was taken over by the General Electric Company (GEC) in 1967 whose Witton Works closed in 1969, with the design office and traction manufacture transferred to Trafford Park, as a result of the GEC reorganisation and mergers. GEC Traction Ltd took over the Works in 1972. In 1990 the former Low Voltage Switchgear site at Trafford Park (West Works) was renovated to be the new manufacturing facility for GEC Alsthom Traction, with an electronics workshop, machine shop and plating baths, and an assembly shop for switchgear, equipment cases and power modules. This building was vacated in 1998 when power modules and switchgear was moved to Tarbes in south west France. The Works housed the administrative, commercial and accounting functions, the majority of the design departments and the development section with its associated workshops and laboratories. The manufacturing area was devoted primarily to the production of components of traction control and railway signalling equipment. In 1993, as part of the rationalisation of the equipment group, it was announced that the headquarters of GEC Alsthom Traction would move to Preston, leaving only Power Module design and manufacture at Manchester, with the eventual closing of all activities at Trafford Park in 1998. The iconic original Westinghouse building was demolished and the site is now (2015) largely devoted to container handling and logistics operations.

Metropolitan-Vickers Electrical Company Ltd (Metrovicks) built an armament factory on Attercliffe Common in Sheffield, a 9-acre site for the manufacture of traction motors in 1921. In 1923 it was made into a self-contained traction motor factory with its own engineering department and the manufacture of complete locomotives and electric delivery vehicles. Metrovicks merged with British Thomson-Houston Co Ltd (BTH) in 1928 to form the holding company Associated Electrical Industries (AEI) still trading under each individual company’s name. In 1931, Metrovicks bought the whole Attercliffe Common Works apart from the stamp shop which made 4 1/2 acres of single-storey building available for traction work. During the Second World War the Works suffered bomb damage and became the major supplier of dc generator/ high frequency alternator sets for aircraft and a ‘shadow’ factory was set up at Bamford. Together, 140000 sets were produced with military work continued at the factory up to the 1970’s. In 1956 Attercliffe Works became the feeder department for the new AEI factory on Greenland Road also located in Sheffield for the manufacture of smaller type of machines, traction gears. AEI created a subsidiary called AEI Traction Ltd in 1959, which took over the Attercliffe Common works to manufacture traction motors, generators, gears and other machines such as motor-generator sets used for converting the high traction voltage to a safer voltage suitable for train lighting, heating, battery-charging and for the control equipment on locomotives and suburban electric trains. The General Electric Company Ltd (GEC) took over AEI in 1967 and Attercliffe Works became owned by a subsidiary of GEC, GEC Traction Ltd who designed and manufactured a full range of traction machines and control equipment for electric vehicles. All British Railways a/c electric loco motors and motor coach d/c motor orders for Hong Kong and Korea up to the mid-seventies were built at the Works. The Attercliffe Common works closed in 1985 when GEC and the French Alsthom group merged in 1989, and the design and manufacture of motors and inductors moved to GEC Preston works and gears moved to GEC Rugby works.

Metropolitan-Vickers Electrical Co Ltd was the new trading name given to British Westinghouse Electric and Manufacturing Co on 8 September 1919. The predecessor company had sold its controlling share to the Metropolitan Carriage Wagon Co in 1916 in order to gain membership of the Federation of British Industries. In 1919, Vickers acquired the Metropolitan Carriage Wagon Co, along with its controlling share in British Westinghouse, prompting the change in name to Metropolitan-Vickers Electrical Co Ltd. The American owned British Westinghouse had established its English operations at Trafford Park in 1899, and Metropolitan-Vickers Electrical Co Ltd continued on the same site from 8 September 1919. The company was initially known for its electricity generators, later diversifying into the manufacture of steam turbines, switchgear, transformers, electronics and railway traction equipment. The passing of the Electricity (Supply) Act in 1926 provided a boost to the company’s post-war fortunes, with the creation of the National Grid generating demand for the company's products. In 1928, Metropolitan-Vickers Electrical Co Ltd merged with its rival British Thomson Houston Co Ltd, retaining both names for trading purposes. The following year, on 4 January 1929, Associated Electrical Industries Ltd (AEI) acquired Metropolitan-Vickers Electrical Co Ltd and the British Thomson Houston Co Ltd. Again, both trading names were retained, and a fierce rivalry was established between the firms which the parent company was unable to control. In 1931, Sir Felix Pole joined Metropolitan-Vickers Electrical Co Ltd as its new chairman. He oversaw a period of expansion for the company leading into the Second World War. In 1939, seeking a more concise name for the company, the Board of Directors decided upon Metrovicks, which became interchangeable with the official company name of Metropolitan-Vickers Electrical Co Ltd. Under Sir Felix Pole's chairmanship, Metropolitan-Vickers developed new products for the aviation industry and during the war was one of the sites where Lancaster bombers were built. In 1941, the company developed the first British axial-flow jet engine, the Metrovick F.2. Following the Second World War, the company appointed Oliver Lyttelton as chairman, with the aim of increasing the efficiency and productivity of AEI. Despite his success in achieving this aim, Lyttelton was unable to resolve the commercial rivalry between Metropolitan-Vickers Electrical Co Ltd and the British Thomson Houston Co Ltd. During his second period as chairman, from 1954-1963, Lyttelton, now Lord Chandos, oversaw the development by Metropolitan-Vickers Electrical Co Ltd of the first commercial transistor computer, the Metrovick 950. Chandos also resolved to extinguish the competition and internal divisions between Metropolitan-Vickers Electrical Co Ltd and the British Thomson Houston Co Ltd, and both company names ceased to be used from 1 January 1960, with all subsidiaries going on to trade under the name of Associated Electrical Industries Ltd.