"Did you see Melanie Phillips's article?" asks a beaming Brian Clark. "Said that Mary Warnock was setting us on the path to the concentration camp and the gulag. Absolutely barking." Assisted suicide may worry some columnists and Conservatives, but the controversy over euthanasia - I meet Clark as the bill to make it easier is working its way through the House of Lords - is nothing but good news for the author of Whose Life Is It Anyway?. With many TV dramas and several other stage plays (Post Mortem, The Petition) to his credit, he is best known for the hugely popular play - it has been performed in Gujarati, Spanish and Hungarian, to name just a few translations. Tomorrow night, previews begin in the West End of the drama about a tetraplegic sculptor who fights her doctors for the right to have her life-support machine switched off.
While the casting of Janet Suzman as the rough-tongued judge who plays God is hardly surprising, that of the sculptor unable to move arms, legs and neck is unexpected: Kim Cattrall, famous for bed scenes of a more active and less costumed nature in Sex and the City. Those who know Cattrall only as the voracious Samantha, however, can be assured that Peter Hall hasn't cast her solely on the basis of her pulling-power. She has appeared on stage in Strindberg and Chekhov, and, back when she appeared in Porky's or Police Academy, did so not only to pay the rent but to finance a tour of Molière.
Clark, 72, is attending rehearsals, but not as supreme authority - rather, he is as much of a rewrite man as if this were its premiere. "In every play I write there's a thousand different plays, and it's up to the director to decide which he's going to do. The play is tested in rehearsal, and you find its weak points each time. I feel a bit like a journalist today - I had to come up with some new lines so quickly."
The rewriting - "little changes over the years but a step change for this production" - has changed, he says, about 20 per cent of the play. There are now references to Stephen Hawking, Christopher Reeve and Diane Pretty. But Clark says that the more important change is in the character of the doctor who, seeing any death on his watch as a defeat, opposes Claire Harrison's petition. Formerly a sober advocate for his position, he now matches her in banter, deflecting her sarcastic, discomfiting jokes with neat turns of comic phrase. They're more evenly matched, says Clark, now that the doctor is funny, too. "It's no longer a conflict between good and evil but between good and good."
The hospital ward in some ways seems to date from the pre-Thatcher period. "Yes, I had to have people who could speak English, so I couldn't take that into account. But, in a cast of nine, we do have three members of minorities - an Arab doctor, a black orderly and an Indian solicitor."
Left, after an accident, unable to move her limbs or neck, Claire is literally a talking head, a bedridden brain - or, rather, part of a brain. "She thinks with her hands," says Clark, "so the technology she is offered is of no use to her. She's not like Hawking, who uses his head - that's all that hasn't gone wrong with him." When Tom Conti played the role, a lot of women would say to Clark, "How sad that that wonderful, sexy man is paralysed." "I asked myself," he says, "'Would it be any different for a woman?'" He found out when, on the play's transfer to New York, the lead was played by Mary Tyler Moore. "I hardly had to rewrite it. But I do think that, with a woman in the bed, the play is more universal. Women are more rooted, they're the carrier of the species, so with a woman it's more powerful."
A woman who needs constant attention, though, may be making a more realistic decision by choosing suicide than a man. Claire, who has sent her boyfriend away, tells her doctor, "He's a healthy man. He should have a baby, a real one." But is she altruistic, or just farsighted? Bedridden or not, most women realise that the male capacity for sacrifice and drudgery lags some way behind theirs. And, unlike women, men retain their sex appeal in the most extraordinary circumstances: despite being confined to a wheelchair, Quentin Crewe, for example, did all right. Hawking, no Adonis, may be able to use only his brain - unlike Claire, he does not even have a natural voice - but that didn't prevent his marriage ending when another, younger woman saw him as a love object. Clark doesn't think this is fair: "It may have been the case that only women took care of the helpless, but that is changing. Increasingly, men are beginning to do it."
Clark's play wasn't the first about the morality of suicide or euthanasia in connection with the severely handicapped or terminally ill, but it was one of the earliest of the award-winning dramas on these subjects that were written from the mid-Seventies to the late Nineties. England produced Duet for One and A Day in the Death of Joe Egg. American plays include Shadow Box, As Is, 'Night, Mother and Wit. One could regard their success as a tribute to the increased sensitivity to the value of every life or, more cynically, to the plays' bracingly cold comfort, as they depict a situation in which members of the audience are unlikely to find themselves.
Clark, however, would not include Whose Life with all the others. It belongs, he says, with works about free will in a world in which the brain - or man himself - is seen as simply a type of machine, one often inferior to the kind that plugs into the wall. It reflects the fear that those who claim to be more knowledgeable about our minds than we are will be able to control us.
Claire, who must prove her competence to make her final decision, says that the process is a catch-22: if you're clever and sane enough to put up an invincible case for suicide, it demonstrates that you shouldn't be allowed to die. And the doctor has more than fact and logic on his side: when Claire becomes too argumentative, he prescribes a sedative. "So I get the tranquiliser," she says, "and you get the tranquillity."
"In the late Sixties and early Seventies," Clark says, "there were more and more technological developments to keep people alive. But what if they didn't want to be kept alive? I thought. Well, then they can kill themselves. But what if they can't? When I thought that, I knew I had a play.
"My play is not about death," he adds. "It's about freedom. Some people could call it a tragedy, because it's resolved by the death of the protagonist, but I think it's a comedy because she's seizing her destiny in her own hands, and that's good. I see the play as life-affirming. In contrast to the 'pro-life' lobby," - he makes a face at the word - "I'm saying there's more to life than just breathing. I find the position of religious people appalling, partly because they want to impose it on me." Clark's background is Episcopalian, but he is now an agnostic, "only because you can't prove a negative".
Clark has had no experience of a loved one's being kept alive artificially, but has made a "living will". "I don't fear being in that situation myself, but I do suffer from claustrophobia - though in dreams rather than in daily life. All my nightmares are about being trapped in a box." Whose Life apart, Clark is working on "a couple of plays. But I don't want to talk about them." He smiles. "I want to keep them in the box."
'Whose Life Is It Anyway?', Comedy Theatre, London SW1 (0870 060 6637) from tonight; booking to 30 AprilReuse content