Rachel Weisz, mixed-up child of Jewish intellectuals, pin-up star of Scarlet and Black, has come of age in the West End's risqu Design for Living. By JESSICA BERENS. Portrait by JAKE CHESSUM
Weisz is pronounced Vice. Rachel Vice. A good name if one should ever wish to front a thrash-metal band out of Detroit. She thought she might change it to the more controversial option - she was bored of endlessly spelling out Weisz on the telephone - but in the end it would probably be more of a hindrance than a help.

She is 24, and this month her name is in lights for the first time. "Weisz", in red neon, appears on the Gielgud Theatre in Shaftesbury Avenue; below Rupert Graves but above the title, Design for Living, by Nol Coward. "Rupert is more famous," she smiles, "but I am the star." Coward would have liked the joke.

And indeed, she is. Reviewers have said "Devastatingly Sexy", "Wonderfully Vicious", "Fiercely Fashionable". The Daily Mail has asked, "Is there an actress on the London stage at the moment who radiates more ambivalent sex appeal than this woman?" She has won the Critics Circle Award for Most Promising Newcomer.

Her role has been described as that of a "feral female catalyst", and tonight, in her dressing-room, she looks the part in her black silk teddy with cream lace floating over seamed stockings. In the last act, as Gilda, she discards her ball-gown in a New York hotel while Otto and Leo persuade her to leave her nice but boring husband, Ernest, and live with them in an erotic mnage--trois. Ernest, unsurprisingly, thinks this very disgusting. The three young decadents yelp and writhe and end the scene in each other's arms.

Black hair that was lacquered into a helmet for Act 2 is now brushed out. In front of her mirror, a lily stuck in a Lucozade Lite bottle sits amidst the aids to dramatic maquillage. A copy of the Big Issue lies in the bin. "It was a bit scarey tonight," she says, brushing and wiping.

"On some nights, it is just funny, but sometimes we really look at each other and take each other in."

Rupert Graves puts his head around the door and says goodbye. For three hours they have loved, tormented and embraced each other. Now, with hardly a word, they separate and rush out into the Soho night, past the noticeboard with the letter from director Sean Mathias ("My glittering monsters, I think of you and send everyone a big hug, not just Rupert"); and past the stage-door-johnnie with the moustache and the programme for Rachel to sign, who makes one want to weep out loud.

The triumphant, shouting style of Gilda softens and becomes Rachel's. Sometimes, coming off stage, she is like a crack addict. "Tonight, I'm reasonably calm, but some nights are so high that if you speak to anyone who hasn't been on stage, they think you're a pain in the ass."

In 1925, Nol Coward noted that "sex, being the most important factor of human nature, is naturally and always will be the fundamental root of good drama". This priority is slightly unexpected from a man who appeared to love only himself and his mother, in that order. The life-stories of Nol, mainly written by Nol, promote a boy from Teddington who liked a laugh, who was urbane from the age of nine, and who went on to spend his free time having lunch with the Queen Mother. But they detail no lust. When he had a nervous breakdown in 1926, it was caused not by passion but by overwork and bad reviews. He woke up in a hospital in Waikiki and missed his mum.

His friendships, perhaps as a consequence, were sometimes complicated. Esme Wynne and Lynden Tyson made the mistake of taking the playwright on holiday before they got married. Such was the platonic intimacy of Esme and Nol that the fianc, inevitably, felt rejected. The engagement was nearly broken off when one morning Tyson saw both of them coming out of the bathroom together. Later, Coward made friends with the actors Alfred and Lynne Lunt, for whom he wrote Design for Living. It was staged in New York in 1933 with Coward as Leo. The trio became so attuned to each other that they could alter speeches and moods. During one scene, Coward and Alfred even found themselves speaking each other's lines.

"I have had to imagine what it would be like to live with two men," says Weisz. "It would take an extraordinary amount of energy to sustain it. There would be no moments when you could relax; one person is always left out. The good side is that you would never be bored. You would get everything sexually, but not much security, so I guess you would have to be kept high on that danger."

Weisz's background is Hampstead Jewish intelligentsia - "quite a weird family, really". Both refugees from Thirties fascism, her father, from Hungarian stock, is an inventor; her Austrian mother a psychotherapist. She says that there were many secrets in the house. Her mother's clients were treated in a room forbidden to Rachel and her sister Minnie, who had to stay strictly silent when a patient was visiting. Occasionally, they could hear weeping; but they never spoke to the strange people who wandered in and out of their house.

"We'd hang out the window and stare at them," she recalls. "I remember one, we called him the Porsche Man - he drove a red Porsche."

It was difficult, sometimes, not to be jealous. The Porsche Man and the others got the attention.

When she was 15, her father left home ("Talk about drama!") and did not come back. He took his daughters for Sunday walks, but never revealed where he was living; he had escaped to a secret place and did not wish to be found by his wife. "My mother would hide in the bushes, trying to listen to what we were saying."

She went to boarding school at Benenden, a troubled time for Rachel, during which she sought analysis and was refused by her mother: "She always said that, at the end of the day, it was best not to know." St Paul's School for Girls followed ("the headmistress hated me"), and then Trinity Hall, Cambridge, where she read English. She started a student theatre group, Talking Tongues, and made the hajj to the Edinburgh Festival with an improvised piece named Slight Possession. "We wore little floral dresses and threw each other around the room," she says. "It was very violent."

Slight Possession won a Guardian award, and Weisz went on to play a grande horizontale at the National Theatre studio. The casting director from the Donmar Warehouse saw it, and she became Gilda.

Ambitious? "Very." She would like to do more theatre - Isabella in Measure for Measure, perhaps, Cleopatra when she is older. But already she has tasted fame on television, playing the 17-year-old aristocrat Mathilde in a romping version of Stendhal's Scarlet and Black. There were open-top carriages and stately homes, but the visual feast was the last scene. In a cave lit by hundreds of candles, Mathilde nurses in her lap the decapitated head of her lover, Julian - actually, the real head of actor Ewan McGregor, carefully positioned between her legs.

Her boyfriend, Jason Shulman, youngest of the Shulman clan and the art director at Harpers & Queen, was greatly taken - "He stalked me, as he puts it." They now live together in West Kensington.

Her personal style is Sixties - short leather coat, hairband, baby-doll dresses - and her milieu is west London boho, a milieu curiously echoed in Design for Living. Graves's delivery, as the painter Otto, is often reminiscent of those who lounge with careful insouciance in the bars of the Portobello Road: monied, bright, shallow and self-destructive; nowadays, fascists wear little pink T-shirts saying babe power.

"You're going out with a Jewish girl?" a fashion witch said to Weisz's boyfriend in the Ladbroke Grove restaurant 192, and grimaced: "Doesn't that worry you?"

Weisz shrugs. She quite often comes across anti-Semitism. "I tend to think they must be joking."