United Kingdom - 1977
Director - George Harrison Marks
This film gets pretty low ratings online which is unfortunate considering the "entertainingly funny and blushingly saucy" poster artwork attributed to Tom William Chantrell, a British artist whose work you can see more of at Britposters.com. Without buying the film there seems to be no way to verify its low quality except for the usual blanket statements about British cinema.
You can see this poster on the wall in a scene in Jack Hazan and David Mingay's Clash socio-bio-pic Rude Boy.