(home movie footage, c1976)

Home movie compilation from a visit to Britain. Robbins Barstow documented every aspect of his Connecticut family's life in home movies, and the results are now held by and viewable at the Center for Home Movies . This particular movie looks at a trip to Britain, mostly filmed in London.
Arrival at Heathrow is punctuated by a rather burnt-out view of a reversing British Airways Leyland Atlantean/Roe coach, GML850J (I've adjusted this screencap):

Better seen is DM1177 (KUC177P), a crew operated version of London Transport's DMS class Daimler Fleetline. It's operating route 24 from Chalk Farm garage, which dates the footage as between 1976 and 1978. There's also a similar Fleetline approaching Victoria Bus Station:

Within sight of Trafalgar Square, an Obsolete Fleet open top BMMO D9 passes a Plaxton bodied coach:

Piccadilly Circus; an AEC Routemaster and a Daimler Fleetline:

From the footage it appears the family took a tour on this Frames Tours coach. CAR165K is a 1972 AEC Reliance with unusual dual-door Plaxton coachwork: