(1970, Sid James, Kenneth Williams, Charles Hawtrey et al)

An early scene features a Thames Valley Bristol Lodekka FS/Eastern Coachworks followed on a roundabout by a London Country AEC RT; the front destination indicator has been faked up to show 'Guildhall'.

Bob Palmer believes this was shot on the roundabout outside Slough Bus Station.
The interior of the Lodekka is also shown:

(thanks Clive Lacey and Grant Morton)
A Duple Commander-bodied coach is also glimpsed at a railway station identified by Mike Lloyd as Windsor, and a London Country AEC RF appears on route 458: