(British Transport Films, 1963)

Despite the title, this has bus interest.
Midland Red 3724 (NHA724), a 1950 BMMO S10/Brush. That might be a similar vehicle following:

Several London Country AEC RTs at Stevenage; only one identifiable is RT1062 (JXN90):

West Yorkshire DX10 (MWY119), a 1954 Bristol Lodekka LD6B/Eastern Coachworks, at Keighley railway station:

Morris's HTM557, a 1950 Commer Avenger/Thurgood new to Baxter of Moggerhanger: