Fairly Secret Army (Channel 4 sitcom, 1984-6)

Gentle show about a supposedly secret organisation formed to fight the forces of anarchy, starring Geoffrey Palmer reprising his stuffy ex army officer role from 'The Fall and Rise of Reginald Perrin'. The title is a nod to the wartime Resistance drama 'Secret Army', which was itself mercilessly lampooned by the sitcom 'Allo Allo'.
Episode 2.05: Ever Tried Making Love to a Marxist?
Appears to have been filmed somewhere in the Home Counties, and I would surmise the Leyland-National seen in the background of this scene is from London Country, particularly as a Park Royal bodied Leyland Atlantean AN68/1R is glimpsed later in the episode: