The Associated Equipment Company, or AEC as it became known and was most commonly referred to, grew out of a reorganisation, that occurred a few years before WW1, of the London General Omnibus Company or LGOC that could date its origins to the mid 19th century
Ostensibly a chassis and engine/running gear manufacturer, AEC became one of the most successful and prominent suppliers of running-units in the truck and bus industry, supplying London's transport and many other companies and countries besides. From 1933 it was based at Southall in west London through to its eventual closure in 1979.
But in 1948 it formed ACV, Associated Commercial Vehicles Ltd., by the amalgamation of itself with the Maudslay & Crossley concerns, although these were left largely independent, whilst AEC continued to be a major force in the truck industry. Shortly thereafter though, ACV was to take over the coachbuilders Park Royal Vehicles creating the "happy marriage" of running-unit manufacture and coachbuilding expertise. This combination was so formidable in the bus and coach industry that it was unstoppable in winning major contracts both throughout the country & worldwide and went on to provide, almost exclusively, London's buses (including the Routemaster) for the next thirty-plus years.
The involvement of Leyland from 1962 was not of itself significant, but Leyland's later nationalisation after its disastrous attempts to return to profitability Britain's car industry, was. And thus, after much right-sizing (the euphemism for plant closures and job losses) by 1980 both AEC and PRV were no more.