In a strange way, says Martin Sherman, he wishes — “quite against my own wishes for financial stability” — that his play Bent wasn’t being performed again; that gay life had fundamentally moved on from nearly 30 years ago when it was first performed. But his story of two men fatefully falling in love in a Nazi detention camp is being revived in a new production at the Trafalgar Studios in London. Back then it shocked because it told of horrors we knew nothing about; today, he hopes, it might shock gays out of complacency.

“In the Seventies we thought we had progress but gays were being discriminated against,” Sherman, 67, says. “There were bars, clubs. There was commercial progress, a lot of people were making money out of gays, but not social progress. When I wrote it I remember seeing gay men wearing Nazi uniforms in Greenwich Village which shocked me. I wanted to say, ‘Don’t you realise what you’re doing?’ Beneath all that talk of liberation there was such self-hatred. There was no real freedom or real inner joy about who we were.”

There is a concordance today, he claims. Sure, gays have greater social equality than ever before: the age of consent is equal, the ban on us serving in the Armed Forces has gone, we can register our partnerships, we’re on the soaps. “But look at the rise of the drug crystal meth on the gay scene, look at the increase in barebacking (unprotected anal sex). There is still that element of self-destruction, of self-hatred.”

By pointing out such uncomfortable, tangled home truths, Sherman runs the risk of being accused of being a killjoy. But recently I spoke to a group of gay twentysomethings who knew (and cared) nothing about the Stonewall riots, the fight for the age of consent, Section 28, the lack of visibility of gays in popular culture until relatively recently. Hopefully, they might go to see Bent.

The play is not some ranty gay rights polemic. The hero, Max, is as much an anti-hero; one who murders his first lover under the eyes of the Nazis. He has sex with the body of a dead woman to prove his supposed heterosexuality. Then, in the detention camp to which he has been sent, he falls for a fellow prisoner, Horst. The scene in which they have sex without speaking was shocking in 1979 and it remains so, as is the manner of Max’s “liberation”, his coming out in the direst circumstances.

Alan Cumming plays Max, a brave piece of casting considering that his memorable characters to date have been mostly outrageous and comic. “The public perception of him is that he is very funny, and he is,” says Sherman. “But he is also a very serious actor with great emotional depth.”

The British productions of the play,which have starred Sir Ian McKellen and Michael Cashman (and a film starring Clive Owen), seem always to have coincided with key moments in British gay history — the heady days of the late Seventies before Aids (and just before Thatcher’s chipping away at our civil liberties), then as Section 28 made it on to the statute books, and now, just as gays have won the right to register their partnerships. It is both a piece of gay history and a marker of the same.

But it must be odd, still lugging this play around 30 years on from when it was first performed. Sherman, however, insists that “Bent is no burden, it quite literally saved my life.”

He was born and raised in Philadelphia. From the earliest he can remember he wanted to be a playwright or an actor. His mother started taking him to the theatre when he was 6. Then she became ill, he says quietly, and he started going on his own.

He remembers, aged 12, watching the work of Tennessee Williams, “with material on all kinds of sophisticated levels that I didn’t understand but at some intuitive level I did”. He saw the first production of Cat on a Hot Tin Roof, recalls Williams and the famed film and theatre director and producer Elia Kazan sitting a few rows in front, “and I wondered what would happen if they turned around and saw me, this strange 12-year-old kid”. He started writing plays, too, including one that featured the three witches of Macbeth made nice. “The theatre was a lifeline. I had a very unhappy situation.”

His mother suffered from the debilitating Huntington’s disease, “the worst disease in the world”. “My father’s family were peasants from a shtetl in Russia so it was not something they knew how to handle in a mature way,” he recalls sadly. “They took all the superstitions from the shtetl — about not being able to engage or deal with disease itself, and also that the medical profession couldn’t deal with disease.”

Sherman’s mother withdrew into the shadows of family life until she lapsed into a vegetative state. A nurse moved in to the family home. Sherman Sr married again two years before she died, when Sherman was in his late twenties (“I’m one of those lucky people to have a fantastic stepmother”). In his mid-20s he had a therapist who told him that of all her patients, Sherman had had the worst childhood. “According to everything I have read,” she told him, “you should be institutionalised. Not only are you not, but your two feet are planted very firmly on the ground.”

Sherman trained to be an actor. “I discovered that I wasn’t very good because I wasn’t comfortable with myself,” he says. “You need to have a certain sense of who you are to be a good actor.” But it gave him the ability to master “the actor’s language” as a playwright. Bent really was a “lifeline”: for nearly ten years he had tried in vain to get his plays put on. He was “depressed, desperate, I was thinking, ‘I wish I knew how to do something else.’ ”