Prime Suspect 1973.
Rover P6's, Austin 1100, Vauxhall Viva etc.
Lex Shrapnel. What a fucking ace moniker
I just watched ep. 2. Would the uniformed rozzers really be using a 1966 Rover in 1973?
I know it jars a bit when they get these things "wrong" but...
You are watching an fictive portrayal of imaginary events, i.e. an grate big fat lie, and in order to make this lie more believable an certane amount of smoke, not to say mirrors, must be employed. However the purveyors of this lie not having an unlimited amount of money for smoke, mirrors or other devices of mass distraction expect you, a willing participant in the lie, to focus not on the set dressing but on the lie itself AKA "the story".
Besides for stuff set in the 1970s you've got the almost insuperable problem that any* motor vehicle built in the 1970s is now a smear metal oxides in the mud of a scrapyard somewhere so you're going to have to use whatever you can get your hands on that's not completely anachronistic.
*May contain traces of exaggeration.