Keith Nason asked about an advert for Norwich Union Insurance made in the 1970s. This featured 39 single deckers from different National Bus Company operators. Leyland-Nationals, Bristol REs and Bristol LHs were used:
The only registration plate identifiable from the Youtube footage I have seen is for Lincolnshire Road Car's 1033 (WFE678M), a Bristol LH6L/Eastern Coachworks:
The closing scene features an open top Bristol Lodekka FLF:
(this may be the advert referred to under the National Bus Company heading)
Chris Hough notes a Norwich Union campaign for personal insurance cover features occasional East Ender Ross Kemp almost mown down by a passing bus, a Dennis Dart/Plaxton of Imperial. It appears to be the one previously used in the National Lottery advert filmed in Uxbridge.