Episode 8:
Glimpsed on the road in London are: Timpsons 554GKX, a 1964 AEC Reliance/Harrington Grenadier; a 1966 East Kent AEC Reliance/Park Royal coach; a couple of London Transport Routemasters; a brown Ford R192 or R226 with Duple body, also a blue Bedford/Duple, probably a YRQ.
Episode 10: A Southdown Leyland Leopard/Plaxton.
Episode 12: a London Transport AEC RT.
Episode 13: a pair of BEA AEC Routemasters in orange/white livery, at least one towing a trailer.
Episode 16: behind the opening credits is briefly seen what appears to be a silver Leyland Titan PD2 or PD3 parked on a London street.
Episode 20: A brief evening shot of a London Transport AEC Merlin.
(data drawn from my own observations and reports at the Internet Movie Cars Database