(1973, Ronnie Corbett, Beryl Reid, Arthur Lowe et al)

Film version of the successful stage play - “includes views of many different types of buses in Windsor at the beginning of the film, including RT, RML, etc, and a Thames Valley FLF.” (thanks Bob Tibble).
Although the film's storyline seems somewhat quaint now, it has some wonderful footage shot in the streets of Windsor. The 1965 Thames Valley Bristol Lodekka seen in the opening is FBL485C, new as D21. Also in shot is a London Country RP-class AEC Reliance/Park Royal:

As the Lodekka passes, the RP begins to pull away from the kerb. Also in picture is a London Country AEC Routemaster in National Bus Company green livery; glimpsed behind it is a rare SMA-class AEC Swift/Alexander:

Many other buses are seen in passing, including London Country RMs and SM-class AEC Swifts:

There's a second Thames Valley Lodekka, an older FLF:

….also a Bristol LS in traffic:

This bus behind Cheryl Hall is almost certainly a Bristol LH: