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.

The British Westinghouse Electric and Manufacturing Company Ltd was formed in 1889 by George Westinghouse as a manufacturing subsidiary of the American Westinghouse Electric and Manufacturing Company, of Pittsburgh, USA. Initially it was an agency for American exports, based in London. From 1902, the company was operating in newly-built offices and factory at Westinghouse Road, Trafford Park, Manchester. Products manufactured 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. By 1916 British Westinghouse felt that the American ownership of its operations during World War One had been a hindrance, so a British holding company was created to obtain the American shares. In 1917 the Metropolitan Carriage, Wagon and Finance Co provided the capital for British Westinghouse to become independent of US control. Finally, in 1919 Vickers Ltd acquired the Metropolitan Carriage, Wagon and Finance Co and with it the British Westinghouse business. Vickers wished to be able to supplement their production of steel, ships, trains, and machinery with that of the associated electrical equipment. The company name changed to Metropolitan-Vickers Electrical Company on the 8th September 1919.

Associated Electrical Industries (AEI) was formed in 1928 as a financial holding company for a number of leading electrical manufacturing and trading companies in the United Kingdom. The two major constituent companies were British Thomson-Houston (BTH) based at Rugby, (Mill Road Works) and Metropolitan-Vickers Electrical Company Ltd (Metrovicks) situated at Trafford Park, Manchester. However, fierce rivalry existed between the Metrovick and BTH brands resulting in internal competition and duplicated management. This was highlighted during the Second World War in 1939, when Metrovicks and BTH became the first two firms in the world to construct jet engines (independently from each other). Following the Second World War, in 1954, AEI expanded to consist of BTH, Metrovicks, Edison Swan Electric Co, Ferguson Pailin, Hotpoint Electric Appliance Co, International Refrigerator Co, Newton Victor, Sunvic Controls, Premier Electric Heaters, Siemens Bros (1955) and Birlec (1954). In 1959 AEI decided to remove the familiar brands of BTH and Metrovicks and consolidate both as AEI resulting in internal problems and a fall in sales and market value. However, AEI acquired a variety of companies from 1959 to 1967, these included Associated Insulation Products, W. T. Henley’s Telegraph Works Co (1958), and London Electric Wire Co and Smiths (1958), Submarine Cables, Hackbridge Holdings Ltd., The Lancashire Dynamo and Crypto Ltd., W.T. Avery Ltd., Henley and Schreiber. The General Electric Company bought AEI in 1967.

The British Thomson-Houston Co. Ltd., (BTH) was created as a subsidiary of the General Electric Company, USA in 1896 to exploit the sale of products in the United Kingdom. BTH was a reconstruction of an existing firm, Laing, Wharton and Down (1886). The BTH manufacturing works were based at Rugby, Warwickshire and the company’s products included induction motors, alternators, switchgear, turbo-generators and turbines, as well as a large number of rotary converters and motor converters, primarily for chemical plants. During the First World War, BTH’s most significant contribution was the development of marine apparatus for the naval service. The 1920s saw a period of vast expansion for the company with new extensions built at many of its factories such as Willesden, Birmingham, Chesterfield and Lutterworth. BTH amalgamated with Metropolitan-Vickers Electrical Company Ltd to form Associated Electrical Industries (AEI) in 1928 although both companies retained their separate identities and continued to compete for the same contracts. BTH developed manufactured electric torpedoes and electrical components for aircraft engines, munitions, etc., during the Second World War and in 1935 independently of each other, BTH and Metropolitan-Vickers were the first two companies in the world to construct jet engines.