Mona Lisa (1986, Bob Hoskins, Cathy Tyson, Michael Caine)

Shot in and around London and Brighton - no buses are part of the central action, but there are some guest apprearances in the background:
As George (Hoskins) drives through an underpass, a Leyland B20 Fleetline is seen briefly. In another scene a London Transport Routemaster RM on route 19 passes; and a scene in Park Lane has two RMLs as a backdrop.
Unexpectedly a Duple-bodied Whippet of Fenstanton coach is seen parked - speculation: is this DAF A809REW?
Also a Plaxton-bodied coach belonging to Excelsior of Bournemouth.
Jon Price notes "Towards the end of the film when Hoskins and Tyson park outside a hotel in Brighton, a Southdown two door Bristol VRT/Eastern Coachworks in National Bus Company green with a Tesco wrapround (Unibus) advert comes across the front of the shot."