Features Red Rover, Aylesbury, 3 (KGK741), an AEC Regent III RT/Craven formerly London Transport RT1482 (thanks Mike Lloyd):
This bus also appears in The Boys (1960).
This standard AEC RT is glimpsed:
....and it's a shame we don't get a closer view of these two; the left appears to be a Barton coach, while Bob Wingrove identifies the right as one of a small batch of private hire London Country RFs, RF16-26: "the last of the batch of private hire buses that were converted to Green Line use. (only 5 windows and a rear instead of 6 and a rear, and you can just make out the observation windows in the roof)"