The Lickerish Quartet Movie Review
The story itself is a bust: Four people in a proper British manor couple in various formations; the blonde girl they (mother, father, and son) picked up at the local fair because she looks like the girl in the sex film they like to watch. The ending doesn't quite pay off the promise of epic violence or a bizarre coupling... instead the film serves mainly as mood music for its entire running time.
If watching '70s sex scenes (the pubic hair styles alone are worth the price of admission) is your cup of tea, well have I got a movie for you.
Available as part of the Radley Metzger Collection #3 box set with Carmen, Baby and The Princess & the Call Girl.