My father once owned a 1970s Blue Morris Marina van, the cars look good klambert.
As for the best 1970s British car, one of my schoolfriends in 6th form ran a Triumph Stag, and yes, his father was "loaded" to be able to buy one for him.
However, to my mind the commonest cars of the 70s in the UK have to include the Ford Escort MkI (1968-74) & MkII (1974-80), Ford Cortina MkIII (1970-76) & MkIV (1976-1982), plus the Ford Fiesta Mk1 (1976-83).
I think that the Police even had a couple of Ford Fiesta "Panda" Cars in light blue in the late 70s/early 80s.
Two "rare birds" I clearly remember close by my home during the late 1970s, a Ford Capri John Player Special and a Reliant Scimitar.
As for a non-UK car vividly in my memory another of my 6th form classmates had an early 70s yellow Datsun Cherry and I recall having to help him push start it one cold winter's evening when there was snow on the ground!