(Granada TV crime drama, 1976-7)

According to this drama, males born with an additional Y chromosome are thought to be genetically inclined to criminal behaviour. Seen in the opening credits are fragments of London Transport AEC Routemasters and an AEC Merlin:

Episode 1.01: The Proposition
An opening set in Manchester includes this Greater Manchester PTE 'Mancunian' Leyland Atlantean:

Episode 1.02: The Execution
A London Routemaster glimpsed….

..then, in the company of another RM, Obsolete Fleet OM1 (903KHA). Before conversion to open top for sightseeing duties with Obsolete Fleet in London, this BMMO D9 was 5016 (3016HA) in the Midland Red fleet. The Midland Red.net website notes that at some point while with Obsolete Fleet the number plates for OM1 (903KHA) and OM5 (3016HA, formerly Midland Red 5016) were mixed up and the error only noticed when OM5 was preserved by the BaMMOT Museum.

I'd guess this is OM1 again; it's passed by a succession of Routemasters while parked:

Episode 1.03: The Resolution
No id for this passing Plaxton coach: