Set and filmed in Liverpool. These low-quality caps give a flavour.
Seen here is Liverpool Corporation L303 (VKB834, a 1957 Leyland PD2/20 with Crossley body), which is passed by Ribble 1476 (JRN43, a 1956 Leyland Titan PD2/12/MCW):
When Stanley Baker's character disembarks, we see L271 (VKB727), another 1957 Leyland Titan PD2/20/Crossley, behind him:
It's unclear what this single decker is, but the fleetname starts with 5.
Another Ribble Titan waits outside a school:
Thereafter a number of Liverpool Corporation buses are seen in background, but none clearly: