That BOAC bus was hired for the spectacular BA "To Fly To Serve" television advertisement of a couple of years ago where they had aircraft from the original DE Havilland biplane through to Concorde. It appeared in the background of the BOAC VC10 at Duxford. Looking at the picture above, it could well have been shot at the same time.
The BOAC buses were maintained by the airline itself at the MT garage on the Northside. The BEA ones were provided by London Transport from a garage at Chiswick. TWA also had double deckers, managed by coach company Halls of Hounslow. These are probably the least remembered, so here's a photo to add to the above.