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.

In 1959 Associated Electrical Industries (AEI) created a self-contained company named AEI Traction Division to control the railway activities of both Metropolitan Vickers Electrical Company Ltd and British Thomson-Houston (BTH). Included in this company were the interests of the Metropolitan-Vickers General Railway Signal Co., (later to become GEC General Railway Signal). The newly formed company established its headquarters, at Trafford Park, Manchester, and operated from three other sites, Attercliffe Common in Sheffield, Rugby Works, and Stockton Works supplying traction motors, machines, control gear and mechanical parts of locomotives. AEI Traction Limited’s product range encompassed electric and diesel-electric locomotives; electrical equipment for tramcars, trolley buses, trolley mining locomotives, traction motors and gears. In 1969 AEI Traction Division merged with English Electric Traction to form English Electric-AEI Traction Division.