Gwynn is perhaps best remembered for his role in the first episode of the BBC comedy Fawlty Towers "A Touch of Class" (1975) as the conman "Lord" Melbury who eventually humiliates Basil Fawlty. For Hammer Films, he performed in several productions including the war film The Camp on Blood Island (1958), and Never Take Sweets from a Stranger (1960), a rare drama film for the studio; the actor also appeared in one of their very best horror movies, The Revenge of Frankenstein (1958), in which he played a tragic experimental subject who turns into a cannibalistic killer, and the less well-regarded Scars of Dracula (1970) in the role of a priest determined to battle Count Dracula.