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.