Kristin has stage fright

She says: "I try to speak English with the children and they resist. My daughter is totally bilingual, and I am proud of her, but my son is more difficult and baby George doesn't speak much."

Scott Thomas has been described by interviewers as "cool", "icy" and "languid" when probed about her private life. But as she tentatively prepares to step back into the limelight with her West End appearance (she's not been in the public eye since Gosford Park two years ago), the actress appears more relaxed as she holds forth on her husband.

"Francois is a very kind man," she says. "He helps people to have babies, which is a fabulous job. But lots of women wait too long to have kids, putting their career first, and then find they can't."

But didn't she have infant George when she was 40? "It's different when you already have two children," she replies. "I was longing to become a mother again. It was film after film after film, so I stopped and took a year off because I was desperate for another baby."

She won't be rushing into motherhood again despite admitting she's rather sad that her youngest child is growing up so quickly.

So why, I persevere, is she keen to leave this domestic idyll for the London stage? It's evidently not for the fame which she hides from. "I have no intention of moving back to Britain," she once said. "In Paris I can go to the movies, whereas in London people just stop and stare."

The answer is much more simple - theatre is her passion, despite the stage fright. "Acting is what I've always wanted," she says. "I wanted to be a stage actress when I came to France ... but I got side-tracked into being a film actress."

Although she has an array of blockbusters under her belt Scott Thomas prefers to concentrate on projects close to her heart - theatre and French art house films. "That's what not being famous allows you to do, but once you become too starry the agents won't let you," she explains, clearly indicating her preference.

One of four children, Scott Thomas had a privileged family background in Dorset but suffered early tragedy when her father and then her stepfather - both Navy pilots - were killed in similar accidents when their planes crashed into the Channel.

After being educated at Cheltenham Ladies' College (where she says she was miserable) and fleeing to Paris, she made ends meet by working as an au pair and a waitress, before landing her debut role alongside Prince in the 1986 flop Under The Cherry Moon. "I was so appallingly bad," she giggles.

She improved her reputation considerably playing the repressed Englishwoman in A Handful of Dust, before taking the part of Hugh Grant's wealthy wife in Bitter Moon and harbouring unrequited love for Grant again in Four Weddings as chain-smoking wall- flower Fiona.

Despite her critically lauded performances, it wasn't until she played plain Matty Crompton opposite Patsy Kensit's ravishing beauty in Philip Haas's Angels and Insects that she scooped a Bafta Best Actress award.

"The thing I loved about the part was that I didn't have to wear any make-up," she laughs. "It was funny because people were paying me the perverse compliment of saying, 'My God you were really ugly.'"

But in 1996, Scott Thomas chose to confound all perceptions by accepting the role of Tom Cruise's sidekick in Mission: Impossible. The task, she confides, appealed to the eternal child in her. "It was a completely new experience. We had to do this scene in an elevator, so I got in and looked straight ahead. I mean, what else do you do in a lift? The director told me I looked as if I was in some intellectual French movie. So I had to do it again and was pretty embarrassed. The French word for acting is jouer which also means to play - you should never lose sight of that."

Then, three years later she played opposite Robert Redford in The Horse Whisperer.

After her stint in the West End, Scott Thomas will rush back to Paris where she recently started her own production company. She has already purchased the film rights to two books - Sea Change by Elizabeth Jane Howard and AL Kennedy's Original Bliss, about a battered housewife who teams up with a gregarious self-help guru.

With her production company, a modelling career (she's in the spring Armani campaign) and more acting in the pipeline, how, I tentatively enquire, does she seemingly keep hearth and home together so effortlessly? "I try to find a way of working that doesn't make our lives too difficult," she says.

"I wouldn't go to Australia and then Japan in a row for work, for example. That wouldn't be possible for our family life, which is very precious.

"You have to remain incredibly calm and not speculate about the future because it can be a dangerous occupation. It can all evaporate just as quickly as it arrived."

The Three Sisters opens at the Playhouse Theatre on 3 April.