The bus and commercial vehicle manufacturer AEC was based in Southall on a 25 hectare (63 acre) triangular site between Windmill Lane, the main Great Western Railway and the branch to Brentford Dock. The company moved to Southall from Walthamstow in 1926 and closed in 1979 when all British Leyland group heavy truck production was concentrated on a new factory at Leyland with the introduction of a new range. The site was familiar to railway passengers from a large sign saying "Builders of London's Buses for 50 years".

The Associated Equipment Company Limited evolved from the merger in 1908 of the London Motor Omnibus Company - which ran its "Vanguard" buses on services in the capital from their works at Walthamstow - and the London General Omnibus Company.

London's bus chassis of the early 20th Century were mainly imported and the enlarged LGOC. built bus chassis to its own design at Walthamstow Works. The LGOC was aquired by the Underground Electric Railways Co of London Ltd and in 1912 the UERC established a dedicated chassis-building company, the Associated Equipment Co Ltd.

AEC and Daimler merged in 1926 to form the short-lived Associated Daimler Co Ltd, coinciding with construction of the new works at Southall, west of London. The first Southall chassis were completed in early 1927 and over the next fifty-two years AEC were leaders in the highly competitive field of commercial and passenger vehicle manufacture. From 1930, AEC produced new models, the names of which all began with "M": Majestic, Mammoth, Mercury, and so on. These original M models continued in production until the end of the Second World War. AEC introduced diesel engines across the range in the mid-1930s.

In 1946, AEC and Leyland formed British United Traction Ltd (BUT) as a joint venture to manufacture trolleybuses and traction equipment for diesel railcars, since reduced demand would not require the existing capacity of both parents. ACV/BUT lightweight railcars were normally associated with the St Albans - Watford, and to a lesser degree the Harrow - Belmont route. They were not successful and all were cut up by Derby C&W by the end of 1963.

Post war, many thousands of buses, lorries, dump trucks and chassis for fire appliances were built for the UK and export markets, while AEC engines were used in other makes of chassis and for military, marine and industrial use. A further merger in 1948 combined AEC, Crossley Motors and the Maudslay Motor Company to form the Associated Commercial Vehicles Company. ACV acquired Park Royal Vehicles Ltd and PRV subsidiary Charles H Roe Ltd the following year. In 1961, AEC acquired Transport Equipment (Thornycroft). Thornycroft's name disappeared from all the vehicles, apart from specialist airport crash tenders such as the Nubian, and the Antar off-road tractor unit.

The last merger was with Leyland Motors Ltd in 1962. Double deck bus production ceased with the last Routemaster and Regent V types built in 1968. The ailing British Leyland Motor Corporation was nationalised in 1974 and Southall survived until 1979 when the final Marathon goods chassis came down the production line and the works was closed down.

The main Works were demolished in 1981. The former Spares Dept building stood largely unaltered since it was vacated by AEC in 1979, but was demolished in 2005. The former Sports Ground, once protected by Green Belt controls, and the production site now form the Great Western Industrial Estate.