Fond amusement is mostly the point (I think) of this clear-eyed look at a short-lived British phenomenon. Sexploitation films emerged from the burgeoning sexual revolution of the 1960s. Depending on who you ask, this revolution came about as a result of sex between men being decriminalised, or the liberating arrival of the pill for women. All the subsequent shagging coincided with a dip in British-made films, owing to the explosion in popularity of television, which provided audiences with entertainment they could watch in their own homes. But what they couldn’t watch at home – not easily anyway – was pornography, which was still illegal.

A handful of canny film-makers sensed something in the air, combined a furtive nude short-film industry with slapstick comedy, and invented a new and wildly popular genre.

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The documentary is as gregarious and cheeky as the subject matter demands, but it takes a sensitive, contemporary view on it, too, and allows the people involved to explore every side of the story. Among the big questions addressed is whether the female actors were exploited. Some of them say they went willingly and happily; others say there weren’t many other parts for women. Some paint a grimly familiar picture of casting couches and jobs for “favours”, in a heavily male-dominated business. In a fascinating segment, we learn about the one woman who held a position of real power: Hazel Adair, writer of Virgin Witch, Sex Clinic and Keep It Up Downstairs. She also co-created Crossroads.

Its other main query is why the British seem compelled to mix their sex with comedy. In Europe, sex films were sensual, soft-focus and at least aimed to be classy. In Britain, it was ooh-er-missus innuendo, door-to-door salesmen being ravished by housewives and female characters called Busty. There are various theories put forward as to why, from traditional seaside-postcard humour to the stiff upper lip to the fact that “nobody took their clothes off in those days”. I like the producer who blames it on the inherent conservatism of the nation and the old aristocracy. But it never quite settles on a convincing answer. Nevertheless, this is highly entertaining, eye-opening stuff, and it’s only the first part of two. Next week: Joan Collins and The Stud. If those five words don’t reel you in, this probably isn’t for you.