I'm waiting to meet Ludivine Sagnier in a Paris bar called the Comptoir Général, an unsettling warren of run-down rooms, employed as bohemian venues for louche Parisian parties. They're made up to look like different stage sets – a schoolroom, a museum, a cocktail lounge – and I'm standing in the schoolroom, thinking of the startlingly various guises in which I've seen Ms Sagnier.
I've seen her as the tanned Côte d'Azur bimbo in a black-and-purple bikini in Swimming Pool, as the pyjama-clad tomboy singing a song about her Papa in 8 Women, as Tinkerbell in PJ Hogan's Peter Pan, as the gangster Mesrine's moll in Public Enemy No 1. I've seen her wearing a bustle in the 17th-century Molière and wearing nothing at all in Water Drops on Burning Rocks. I've seen her playing overwrought, cute, homicidal, romantic, highly-sexed, childish, teasing and sophisticated. I've seen her in half-a-dozen sex scenes and wondered if it's written into her contract that she must always be on top (or is it just that every director wants to highlight her fabulous breasts?). I've seen her beautiful blue eyes widen with surprise, fill with tears and crinkle with laughter.
Sagnier is one of France's most accomplished actresses and one of modern cinema's finest shape-shifters. At just 32, she's appeared in 33 films, a career that began when she was 10, acting alongside Gérard Depardieu in Cyrano de Bergerac. But blow me down if the slender woman in the star-patterned mini-skirt and micro-jumper, who has been talking to the Comptoir's management for the past five minutes, and who I took to be a teenager, isn't the lady herself.
Sagnier is petite – five feet four? – full of assurance and looks as though she's just emerged from an afternoon nap. Her straw-blonde hair is unbrushed, her voice has a sleepy husk about it, there's something Garfield-the-Cat about her eyelids. She's not a classic beauty but her face radiates intelligent hauteur, and her conversation – in a charmingly quirky English idiolect – is full of the joy of becoming someone else.
This summer, she's racketing about the globe introducing audiences to her two new movies, The Devil's Double and Love Crime. "I was in Los Angeles last week, at the film festival," she says, "and one of the journalists interviewing me, who'd seen both films, didn't realise I was the same actress. 'That was you?' he said. For me, that kind of confusion is very rewarding."
You can hardly blame the guy. In Crime d'Amour, Sagnier plays an uptight young French businesswoman in the grip of a passion for her boss, Kristin Scott Thomas; in The Devil's Double, by contrast, she plays Sarrab, the foxy Arabian mistress of Saddam Hussein's son Uday, in a succession of red, black and platinum wigs, sequinned frocks, diaphanous nighties, false eyelashes and lots of weapons-grade smouldering. Had it been hard to express a real person from beneath all that?
"I wasn't sure at first how I could commit myself to playing an Iraqi prostitute," says Sagnier sweetly. "It's not me. I have Norwegian roots. I'm a young, blonde French girl. But when I met Lee Tamahori [the director] he told me, 'No worries, we're going to make you Lebanese, because they have much lighter skin, more European complexions'. It's true the use of wigs and make-up is strong. But it's part of the pleasure of being an actor – I like the idea of transformation. The less I look like myself, the better I feel."
The film enters the mad world of Uday Hussein – spoilt, tyrannical, capricious, addicted to cocaine, guns and sex with underage girls – through the arrival at his court of an Iraqi soldier called Latif Yahia. Latif bears a startling resemblance to the mad Uday and is drafted as his double, his fiday – literally his 'bullet-stopper'. Latif becomes the mirror image of Uday, watches his mounting excesses with horror, and starts to fall for the seductive Sarrab, who writhes and undulates and gives him come-hither glances in a way that spells trouble.
"In this world, no one is what he or she pretends to be, even Sarrab," says Sagnier. "She was probably picked up by Uday one morning, and has no choice but to play a game like a clown in a circus. I find her interesting because she had to lie to everyone. She's never faithful. She's always hiding behind this sexy image that she's sick of. She's like a lot of women in Middle East countries, who have to deal with male oppression and have to pretend they like to be dominated even if they don't."
Dominic Cooper, the British actor, plays both Uday and his double in the film – one a bravura performance of scarily manic energy, the other a rather muted impersonation of decency under threat. How had they got on?
Fantastically, she says. "The first time we met, we talked about Greek tragedy, because he'd just finished playing Hippolytus in London [in Racine's Phèdre, alongside Helen Mirren at the National Theatre]. Up-and-coming Hollywood actors usually haven't much to do with ancient tragedy... I was happy to discover he'd had huge experience on stage – very useful for the character because Uday is always on stage, taking the whole space for himself, imposing his power on everyone physically."
But how had she found acting with, as it were, two Dominic Coopers? "We had two different relationships," she says thoughtfully. "When he was playing Latif, he was very sweet and understanding, very careful with me on set. When he was in Uday's mind, he was much more playful, cheeky, teasing. There was much more sexual tension going on between us." Sagnier's voice suddenly becomes interestingly husky. "But you know," she says, "actors – they're like dogs."
Come again? "When we get to play a love scene and sexual intercourse," she says, "there's a very nice relationship that's created which has nothing to do with real life, but means you play around with the sexual tension we're forced into. It's like little dogs getting a bit crazy."
You mean like little puppies playing? Or like big dogs sniffing each other's bottoms in the park?
"Yeah," she says with a giggle, "It's almost that, too."
The film was directed by Lee Tamahori, the New Zealand-born helmer of the well-received Maori drama Once Were Warriors and the 20th James Bond movie, Die Another Day. Was he rather different from the French art-house auteurs she was used to? "He'd seen me in Public Enemy No 1, and said, 'You're so good at doing gangsters' wives, I want you to do this, I'm sure you're going to be great'. He called me 'My secret French weapon'. What attracted me to Lee was his energy. He's in his sixties but still like a young punk, who's rebelling against the system and needs to assert his independence. I think that, after Once Were Warriors, he got to Hollywood and did studio movies where he didn't have final cut and didn't have much power. He needed to find his own thing, you know? On set he was everywhere, always moving, very funny. We didn't have a lot of money to make The Devil's Double, and I liked the way he found solutions to problems every day and bounced from a no to a yes."
Did Tamahori's brush with the law come up, I ask. Sagnier looks puzzled. I meant, the occasion in 2006 when he was found on the LA streets, en travestie, allegedly offering a blow-job to an undercover policeman. Did he ever try to borrow any of her frocks? "It wasn't a subject we had much to say about," she says with asperity. "I think that in Europe people are far less interested in the personal lives of artists than in America. In France, I think, people don't care."
there's a very level head on Ludivine Sagnier's mignonne shoulders. She was born in 1979 and grew up in Sèvres, home of the famous vases. Her father was a professor of English language, her mother a secretary with a background in classical literature. Both were "movie freaks. They watched a lot of Hitchcock movies, Frank Capra. We'd watch It's a Wonderful Life every Christmas Eve. One of my favourites when I was eight was a 1930s English movie about Marie Antoinette. All the characters spoke English with these ridiculous accents. I remember Moira Shearer saying, 'Ah shall be queen. Ah shall be queen of France...'."
Her father came from a classical music family and wanted his daughters to play the piano. Ludivine found she had no affinity for it and decided, at the age of eight, to "escape from my failure" by attending drama classes after school and at weekends. Two years later, in 1989, she auditioned for her first film, I Want to Go Home.
Many directors have put the feisty Ludivine through her paces (they include Claude Chabrol) but her name has been most linked, professionally, with that of François Ozon, the young, gay, art-house director for whom she worked in three of her best films. They met 13 years ago, when she was 19. "I was leaving the Conservatory, a young stage actress, intending to do theatre. I'd done a short movie that had won awards, in which I played a teenager who misses her train and follows an old man, who gives her a pill, and they watch The Wizard of Oz all night long. It was," she concedes, "a bit crazy. This movie had been shown in many festivals, and Ozon was showing one of his shorts at the same screening. He called me the next day and said, 'I want to meet you – there's something I want you to look at. It's a Fassbinder play'."
It was Water Drops on Burning Rocks, a four-hander, polysexual ménage. "I remember we talked about nudity because my character has to be naked all the time," says Ludivine, "and I remember one of the first things he said to me was, 'I swear we won't see your pussy'." She dissolves into laughter. "I said, 'Well, yes, let's hope so'. Actually, I ended up completely naked in this movie. I was 19, I was so naïve. I didn't know about having to have a public image. I was doing it only for the experience of the shooting." What was her parents' reaction? "I remember my dad did some [teeth-] grinding after the screening. But my mum was all right. She said, 'That was great, that was a great play, you did well'. They respected my work and I didn't feel embarrassed. But it was awful to hear my little cousin singing, over and over, 'Mummy says you're doing paw-orn, Mummy says...'."
Her relationship with Ozon has had its ups and downs. "When he was planning 8 Women," she says, "I was his accomplice." Ozon used her as a sounding-board for his plan to bring together the A-List of French movie stars – Catherine Deneuve, Emmanuelle Béart, Fanny Ardant, Isabelle Huppert, Danielle Darrieux – to co-star in a spoof murder mystery. Sagnier almost didn't get the job because she didn't take her audition seriously enough. But by the time filming began, "We'd started to sew this relationship. We were very close. We used to call each other after each day's shooting – 'So what did Catherine Deneuve say to you?' – we were gossips, we were like terrible children. There was a lot of tenderness, even though we argued all the time. He wrote the movie Swimming Pool for me."
That movie, a marvellous, teasing enigma in which Sagnier plays a free spirit who may be a murderer or may be a fiction in the head of Charlotte Rampling, changed things between them. "After Swimming Pool, we really got sick of each other. I was too dependent on him, and it's never good for actors to depend on directors. He was too certain that he'd made me up, that I'd done nothing. I was sick of him being my mentor. I wanted to prove that I could work away from him. He was pushing me all the time and trying to manipulate me. I felt guilty about not having suffered enough to be a good actor, because I had a lovely childhood. So I felt that submitting to his manipulation was good for me."
You can, in fact, see it on-screen, in the scene where a stark-naked Sagnier has a tearful delusion that Charlotte Rampling is her lost mother. "I remember Ozon shouting 'It's baaaaad! You're not moving enough! It doesn't work! It's not believable!' I had a fever. I had a temperature. I felt terrible. Charlotte Rampling saved me. She could tell I was getting completely vampirised. She said, 'You don't need this stuff. You must go away from it and save your individualism'. I still owe her for that. Every time I see her we recall this moment of complicity."
Now a mother of two daughters, aged six and two-and-a-half (the first from her relationship with the actor Nicolas Duvauchelle, the second with her husband, the director, Kim Chapiron), Sagnier shows no sign of slowing her hectic career. Dubbed 'the new Bardot' by Playboy and 'the new Deneuve' by Rolling Stone, she fears she may be too old to play a Bond babe (though she wouldn't mind) and would be equally happy doing serious work on stage. Can she do both? Can she really play Shakespeare, Molière and Ibsen on stage and also be the girl clutching the hero's hand and dodging bullets?
"Of course," she says with a sweet smile, "that's exactly what I'm looking for. I like this flexibility. I'm looking for variety in life. When I choose the movies I'll do in a year, I'm thinking: in this one I'm going to be that, then this one – wheeeooosh – I'll go in the totally opposite direction. The further away a film brings me, the better it will be."
'The Devil's Double' is released on Friday