Watch The Lovers! (1973) Official Trailer

I've heard it called some things, but Percy Filth just takes the biscuit

Reprising the television series roles which first made them household names, Richard Beckinsale and Paula Wilcox star as Geoffrey Scrimshaw and Beryl Battersby, a hesitant, inexperienced, young couple attempting to negotiate the sexual minefield of the ‘permissive’ society. This big-screen transfer of Jack Rosenthal’s hugely likeable sitcom sees old-fashioned girl Beryl continuing to slap down the advances of her frustrated boyfriend, whose clumsy attempts to initiate ‘Percy Filth’ suggest he’s not quite up to speed himself! Like everyone else, Geoffrey and Beryl want to fall in love – or they think they do; like everyone else, since Adam and Eve. But Adam and Eve didn’t live in Manchester in 1972…