Catherine Deneuve enters Francois Ozon's new film, Potiche, jogging, in tracksuit. It is, admittedly, an impeccable, blood-red designer tracksuit and she looks like she's just left the hairdresser's salon. But a tracksuit? On one of the world's most enduringly glamorous women?

"That's my favourite costume in film," says the 67-year-old French screen legend, belying her role as the muse of her late dear friend, Yves Saint Laurent.

"People always think when you wear couture clothes it's only evening dresses, but I've been involved with Saint Laurent for 35 years so I have many casual things.

"It's funny because people say they can't imagine me in blue jeans on the weekend. I say, 'Why not?'."

Certainly, movie directors like to play with Deneuve's glamorous image, and to her credit, she has always been up for any challenge. Roman Polanski cast her as a woman well beyond the verge of a nervous breakdown in 1965's Repulsion and two years later, in Spanish maestro Luis Bunuel's Belle de Jour, she played a haut-bourgeois Parisienne who seeks sexual gratification by working in a brothel.

She once wrote to the provocative Dane, Lars von Trier, expressing interest in working with him.

In response, he cast her as a factory worker alongside Bjork in 2000's Dancer in the Dark, which went on to win the best film and best actress prize (for Bjork) in Cannes.

Now in Potiche, a satirical farce on big business and workers' rights, Francois Ozon has her in curlers as Suzanne Pujol, a woman controlled by her industrialist husband (Luchini) until he becomes sick and she must take over the family umbrella factory.

She does so with great aplomb, by adopting a more personal approach, and emerges from the experience a different, emancipated woman.

She even wards off the advances of her former lover, communist and trade unionist, played by Depardieu.

The film, whose title is untranslatable - it is a word for a pretty but useless small vase and is loosely equivalent to the English expression "trophy wife" - adapts a hit French play, first produced in 1980 but set in the 70s. It starred the late Jacqueline Maillan, a household name in France, and director Ozon says that Maillan put her stamp on the role to the extent that it was hard to imagine anyone else playing the part.

"It took me some time to think that Catherine could play the part because she is exactly the opposite of Jacqueline, whose extravagant way of acting is very dated now. Catherine is different: she doesn't want to be superior to her character.

"She was the first one I asked and I she had said no, I would simply not have done the film. I mean, can you imagine anyone else in the part?

"In America maybe Meryl Streep, in England Helen Mirren - but nobody else in France could have done it."

With the playwright's blessing, Ozon wrote a third act, which winked at the campaign of Segolene Royal, the first woman to run for president. "She didn't win," he says, "but in the film Suzanne wins: that is the power of cinema."

But he resisted the temptation to update the setting.

"Doing some research about the 70s and the political context I realised the situation in the play is very relevant today particularly in France. Women are not paid the same, the pensions are lower for women than men. Things have changed [but] there are still a lot of fights for women.

"I had a feeling that it was possible to speak of today and leave the story in the 70s and it gave me an opportunity to keep the comic element; if it was set today it might need to be very dramatic."

Deneuve, for her part, stops short of saying that the film suggests the world would be better if women took over.

"Oh, I don't see why it would be better, but I think it would be better if there were more women in public life with a bigger responsibility, because it's still not very fair the amount of women who are there."

The third of four daughters born to actors Maurice Dorleac and Renee Deneuve, Catherine took her mother's name to differentiate herself from her elder actress sister, Francoise. She left home at 17 and by 19 had given birth to the first of her two children, Christian. The father was director Roger Vadim, Brigitte Bardot's ex, and a man twice her age - it was he who convinced her to dye her naturally brown hair to the blonde with which she is instantly identifiable.

She and Vadim were separated within a month of Christian's birth and later she married British photographer David Bailey, who described their seven years together as "like trying to manage a Maserati when you're used to a Ford".

For Deneuve, one marriage was enough, although she had a relationship with the great Italian actor Marcello Mastroianni, with whom she co-starred in four films. The couple had a daughter Chiara Mastroianni and although they split in 1975 they remained close: she was at his bedside when he died of pancreatic cancer in 1996. Other famous lovers have included Francois Truffaut and Clint Eastwood.

"I didn't exactly decide to have children outside of marriage," she says. "It just happened that way. I could have been living with the father of my child forever, but it didn't happen. You never know how long a relationship is going to last and you hope it's going to work, but I never think in terms of eternity. Today nothing seems to work for a long time in relationships. People get divorced so easily."

The 60s were something of a whirlwind for Deneuve as she ascended to early stardom, though she admits that she was a little naive and unable to comprehend the scale of her success. In the 70s she experienced a career slump, which ended with her appearing in 1980's The Last Metro, directed by Truffaut, who had a decade earlier reportedly declared he wanted to kill himself after she'd rejected him. Her greatest recognition came in 1992's Indochine, where she earned an Oscar nomination for her portrayal of a 1930s rubber plantation owner in French Indochina (Vietnam).

She returned to the limelight a decade later in 8 Women, also by Ozon, an odd mixture of musical comedy and murder mystery, which gathered eight of France's top actresses including Isabelle Huppert, Fanny Ardant and Emmanuelle Beart.

Perhaps unsurprisingly with so many divas in one place, the shoot was fraught - Ozon says Deneuve in particular is the kind of actress who devotes herself entirely to her director and sharing him with other stars didn't work well.

Potiche marks the seventh time that Deneuve has shared screen time with Gerard Depardieu and seeing them dance together is quite something. Depardieu famously said of the actress that "she is the man I would have liked to have been", which presumably counts as a compliment.

Ozon says they made a perfect team. "It was dream to have them together. He loves Catherine, and there is a kind of magical chemistry between them. They are the sort of royal couple of French cinema. Always she's the bourgeois and he's the working-class man. That's how they dance together."

Additional reporting by Peter Calder

Lowdown
Who: Catherine Deneuve
What: Potiche, directed by Francois Ozon
When: Opens at cinemas Thursday

- TimeOut