(1972, Reg Varney, Norman Rossington et al) Two waiters (Varney and Rossington) on the run from gangsters hide out in a film studio (actually Pinewood Studios) and get jobs as stuntmen. This is an excuse for a chaotic romp through many different film genres.
Seen in the background of a scene with Varney dressed in a suit of armour is a Neoplan Skyliner; I'd speculate it's the same vehicle seen in Theatre of Blood:

Director Harry Booth recreated the scrapyard set complete with bus used by the TV show Here Come The Double Deckers (1970) (which he also directed) and had Double Deckers star Debbie Russ reprise her role as Tiger, albeit older than in the TV show. Who would have thought Stan from 'On the Buses' would meet Tiger from 'Here Come the Double Deckers?:

Many other actors from the Double Deckers series appear in the film.
There is also a chase, with our heroes (in drag) and Tiger fleeing in a small armoured car, and they pass what appears to be an RT family bus - it's only a glimpse: