This week sees the beginning of the 25th London Lesbian and Gay film festival, an event that has always seemed to me to have a completely admirable emphasis on mischief, enjoyment and fun. And perhaps no film in this year's festival exemplifies this like the extraordinary lesbian crime melodrama Gigola, set in 60s Paris criminal underworld, adapted and directed by Laure Charpentier from her own novels.

Gigola has some highbrow credentials. It features big acting names like Thierry Lhermitte and Almodóvar stalwart Marisa Paredes and is shot by Theo Angelopoulos's cinematographer, Yorgos Arvanitis – but it really is a fantastically naughty, silly and enjoyable film: uncompromisingly camp in its seriousness and high passion, and one of the very few movies that could be called "pulp" cinema. It's steamy, saucy, racy and suffused with the feeling of wickedness you might get from drinking spirits before lunch or smoking in church. One showing is reportedly sold out, but tickets are still available for the second and I'm hoping the programmers can be persuaded to lay on extra, late-night screenings with Rocky Horror-style dressing up.

Lou Doillon plays a mercurial young girl, very striking in a jolie laide way, who in the film's opening moments displays a fervent sapphic adoration for her headmistress. On consummating this passion, she cuts her hair into a new realist mannish style – she already has the monocle, she says at one stage – and acquires a silver-topped cane which she uses as a sex toy. Armed with a handsome private income, she abandons herself to the sensual lesbian underworld, in which she becomes something like a Dorian Gray figure or a vampire: the "night" is her vocation. She styles herself "Gigola" – that is, a female gigolo, making assignations with an infatuated older woman who adores her kid-gloved caresses and who showers her with cash presents. These Gigola uses to buy out a fellow creature of the night from an Italian gangster's pimp-ownership, in the process falling in love with both the woman and the gangster. She is contemptuous of both her bourgeois mama and her dissolute cringing father, who is in thrall to opium and gambling.

There are some very gamey sex scenes and in some ways the whole film has the structure of softcore porn, with a narrative which exists to facilitate the presentation of sex. Gigola is always sexy, even when it's not about sex. And yet, as I say, Gigola is not really porn but pulp, acted with deadpan panache by Doillon. It's the sort of film that isn't likely to get a conventional release from UK distributors. But never mind. A festival is probably the best place to appreciate it. Catch it while you can.