The London Transport site at Elstree had originally been bought for the Northern line extension to Bushey Heath, as part of the 1930s New Works Programme.

[1] Construction of the railway extension was underway and the tube depot was partially complete at the outbreak of World War II.

[2] The existing buildings were extended and converted into a bus overhaul works over a 53.3-acre (216,000 m2) site, with its own staff canteen, social club and office blocks as well as the famous main building, test circuit and tilt test shed where London buses were subjected to being tilted on an inverter to assess stability.

A small number of changes of body among the RT family of buses was made during the period up to December 1955, at which point the 'works float' system of overhauling was re-introduced after being suspended during World War II.

[3] The post-war standardisation and huge size of the London Transport fleet allowed maintenance along modern production line principles, with work being carried out on a number of buses at once.

This system of standard interchangeable components meant that when the chassis was ready to be rebuilt into a bus, the first available engine, transmission and body that had been 'outshopped' would be fitted.

Whether the original, pre-overhaul combination was retained or not, what was almost always the case was that the overhauled bus would leave the works with a completely different identity - see the paragraphs below on the 'works float'.

This modular system meant that buses could be overhauled in a shorter time than it would take if each bus was attended to on an individual basis.

One of the unusual aspects of the London Transport overhaul process was the "works float" system used for the large classes of buses such as RT, RTL, RTW, RF and Routemaster types.

The smaller classes (RLH, GS types, for example) were not subject to this mass overhaul process and retained their original identities throughout.

After the end of Routemaster production, later 'off-the-peg' buses such as the Daimler Fleetlines were less suited to this style of overhaul, due either to the impracticability or the impossibility of separating body from chassis.

This eventually resulted in a reduction of the workload of Aldenham, with London Country establishing its own overhaul facility at Tinsley Green near Crawley.

That factor, together with increased financial pressures in the bus industry, led to a significant decline in the need for an overhaul works of the standard of Aldenham.

Aldenham became increasingly uneconomic due to a shrinking bus fleet and the arrival of numerous types of non-standard vehicles not suited to full overhauls.

Aldenham was an ambitious project, designed to cope with maintenance of a massive bus fleet and geared to the concept of frequent, comprehensive overhauls - something that dated back to the early days of London's motor buses when the Metropolitan Police (the regulator of the time) required that each wooden-framed bus body be rebuilt every year.

The last film of the derelict works took place in 1992 for the BBC series Perpetual Motion which featured the story of the AEC Routemaster and widely on the changes at London Transport.

The episode featured excerpts from "Overhaul", and later repeated the shots this time of the derelict works with the original voiceover dubbed onto the footage.