Buses on Screen: An American Werewolf in London (1981, David Naughton, Jenny Agutter)

A London Transport AEC Regent III RT is involved in a crash in Piccadilly Circus (thanks Kevin McGowan); note that by the time this was filmed the RT class had been retired from service in London.
Leon Daniels notes ".....we actually had two RTs, one for the famous crash sequence and another one which was part of the 24 car pile up on the approach roads, filmed overnight Saturday night Sunday morning. A close run thing it was too - the sky was getting distinctly dark blue as the famous crash scene (which we did TWICE by the way) was filmed."

RT1677 (KXW323) is seen in the main sequence, on route 38. "By then it had white roundels and appears in the film in a few 'passing' shots. The skid and crash was achieved with balding rear tyres and some speed - made more difficult since the approach was from Lower Regent Street which is uphill!
<
The whole crash sequence was masterminded by Dave Bickers (the former motorcycle scrambling champion of the 1960s, latterly Bickers of Coddenham the coach firm, and Bickers Action Enterprises the film and tv stunt organisation).
....Colleague Tim Hornby and I drove the buses together with, as I recall, Vic Armstrong. Some of the close up impacts, and the passenger coming out of the upper deck window, were done at Brooklands, if I recall correctly." (thanks Leon Daniels)

The second RT may have been RT196 (HLW183); RT1677 also appears briefly in a daylight scene in Trafalgar Square. More prosaically there are appearances by then current London Transport buses, a DMS Daimler Fleetline and another behind an RML Routemaster:

This RML appears on route 14, and RM972 is also seen on route 55:

Buses on Screen > Films > Films A > An American Werewolf in London (1981, David Naughton, Jenny Agutter)