“As near as I can figure out, it’s because I fight and fuck too much,” RP McMurphy (Jack Nicholson) informs the doctor who asks just what he’s doing in a mental institution. He’s 38 years old, with five counts of assault and one of statutory rape against him. “Between you and me, she might have been 15, but when you get that little red beaver right out there in front of you I don’t think it’s crazy at all… no man alive could resist that. That’s why I got into jail to begin with and now they’re telling me I’m crazy because I don’t sit there like a goddamned vegetable.” The prison authorities believe he’s been faking insanity to get off his work detail and have sent him to the asylum. That’s the starting point.

Kirk Douglas was the original RP McMurphy. By all accounts, he was terrific in the ’63 Broadway adaptation of the Ken Kesey novel. The play closed after a few months, but Douglas was keen to turn it into a movie. On a trip to Eastern Europe, he met Milos Forman, and promised to send him the Kesey novel. The book never got through?the censors impounded it. By then, Douglas was too long in the tooth for McMurphy anyway.

Ten years later, Michael Douglas (who’d taken over the rights from his father) and Saul Zaentz again approached Forman. They wanted him because he was cheap and this was a project no major studio would back. Forman saw the material in a different way to his US producers. His experiences in Czechoslovakia gave him an all-too-personal affinity with the downtrodden inmates of the mental institution. “This was a movie about a society in which I had lived 20 years of my life,” he later commented.

One of the reasons Cuckoo’s Nest remains so fresh is that it’s so self-contained: outside forces rarely intrude. There are few specific references to ’60s America. Forman shot in the depths of winter. The crew took over a wing of the Oregon State Hospital. It helped, too, that the craftsmanship was first-rate: everything from Haskell Wexler and Bill Butler’s cinematography to Jack Nitzsche’s elegiac music works perfectly.

Nicholson wasn’t first choice: Gene Hackman and Marlon Brando passed on the role, and Forman briefly considered Burt Reynolds. When the filmmakers saw Nicholson’s astonishing performance in The Last Detail, as the marine escorting Randy Quaid to military prison, they realised he’d be perfect. There are obvious overlaps between the two films: the relationship McMurphy has with Billy Bibbit (Brad Dourif) is similar to that between the marine and his young prisoner?Nicholson the worldly-wise elder brother-type, initiating an ingenuous mother’s boy into the ways of the world.

The film has obvious and lasting appeal to anyone with experiences of institutions?whether schools, prisons or even offices?where characters like Nurse Ratched pull rank. That means just about all of us. There are lurches into sentimentality (the treatment of Will Sampson’s statuesque, catatonic Indian is both patronising and manipulative), but Forman’s satirical eye seldom lets him down. The society represented by Nurse Ratched is soulless and homogenised. Human behaviour is governed by the pills dispensed so freely to the patients and by the ersatz classical music on constant playback. It’s not so much insanity that Ratched and her types are trying to keep at bay as individualism. In such an environment, rebelling becomes a duty. It’s hardly an original thesis, but Forman and co put it across with a freshness that few other movies have ever matched.