Seen in the background is a 'London Transport' Daimler Fleetline (noted by Jim O'Donnell on uk-bus-fleetnews discussion group). Ian Simpson suggests "ex Bournemouth Daimler Fleetline/Alexander, judging by the side destination display layout and the livery style"; some of
these vehicles served in London as DMO class. Keith Baynton comments: "The 'London' scenes bus is most likely to be ex-Bournemouth 186 (CRU186C) freshly painted in London Transport DMO 5 condition. 186 is shown on film with a roof in place, whilst similar 183 (CRU183C)(DMO 2) also in USA is now recorded as a permanent open-topper. Both buses were new in 1965 as Daimler Fleetline CRG6LX/Weymann (to Alexander style) convertibles. Two similar buses are preserved in
the Bournemouth Transport Museum (180 and 187 - DMO 6)"
There's also a stock shot of Piccadilly Circus, with RT family buses: