Photography: Deep waters running still

In Love Etc, Charlotte Gainsbourg is enigmatic as ever. Nick Hasted seeks clarification

Charlotte Gainsbourg looks like a hurt child and a stubborn woman, in the same screen second. In her most famous British film, The Cement Garden, she was the androgynous centre of a parentless family, turning to her brother for sexual affection. In Claude Miller's La Petite Voleuse, she was a split-skirted, thieving delinquent. In Bertrand Blier's Merci la Vie, she walked through a fantasia of violence and abuse. In the Taviani Brothers' Night Sun, her childish sexual wants broke a saint's resolve.

It makes her sound like a sexual rebel, some kind of Gallic Sharon Stone. It's an image made easy by the infamy of her parents, Jane Birkin and the late singer-provocateur Serge Gainsbourg, who cast her in the incest- themed Charlotte Forever!, aged 13. Caught in the whirl of her father's lust for outrage, she was a French media fixture almost before she could talk. Now, she says as little as possible. Every interview is an exercise in shielding her privacy. It's in her films that her daring is to be found.

Today, she's in a hotel room near the banks of the Seine. Her face is softer than on screen, less pained. It looks like her cheek is twitching from nerves, till you see she's chewing her nails. Her boyfriend and co- star in her latest film, Love Etc, the rising young French star Yvan Attal, is with her, to fill in the gaps left by her reserve.

She would rather not say a word about herself. But the director of Love Etc, Marion Vernoux, has no such scruples. Gainsbourg plays Marie, the passive centre of a love triangle. "She really is Marie," Vernoux told me. "She hasn't got that many friends, she's quite a lonely person. Her life is being loved by a man. For her, it was really moving, and disturbing, to recognise in herself all the character's traits."

So, I ask Gainsbourg, is that true?

"I'm not sure I have similarities to the character," she says, in a level, refined English accent. "I think she's much more frightened than I am of letting go of her emotions. I'm not like that. I'm not so frightened of being out of control. But I never try to see what's close to me in a part," she adds, trying to cut me off. "I can identify with everything, but in my imagination." She turns to Yvan.

"Of course you know that when you do a movie, you always use what you are," he contradicts her. "Even Robert De Niro uses what he really is. I think when somebody writes something, then thinks of you, he sees something in you that's like his fantasy, something perhaps you don't even see yourself. All the work of an actor is to forget he's an actor."

Does Gainsbourg agree? "No," she says simply. "I do know I'm acting. I get pleasure forgetting myself. I get pleasure getting lost in my role."

There are things I see when I look at your films, I tell her. In scene after scene, it seems like the world is hurting you, puzzling you, betraying you. Is that something you recognise?

"I'm not sure," she says warily. "It would feel weird to say that yes, I feel that I've been hurt in life, and that hurt's inside me. Maybe it is. But I can't talk about it."

Because you don't see it? "Because I don't want to see it. I don't want to be too conscious of myself."

There are other clues in the films. From The Cement Garden to Night Sun (in which, taken to a priest for a cure, she offers him her breasts instead) the characters Gainsbourg chooses seem unconcerned by taboos.

When British journalists pressed her on the subject of incestuous attraction, she told them quietly that she thought it was natural. So apparently restrained in public, artistically she's her father's convention-crushing equal.

"I'm not easily shocked," she agrees. "I hope I have an open mind, that I can think freely about certain things. Maybe it is because of my parents and the way they brought me up. For me, feelings between people are the most important thing. I hope I see people as human beings, before I think of the social rules they might break."

In one of her early films, The Impudent Girl, she strains against the bonds of family, till she falls back into them, exhausted. In The Cement Garden, too, there's a longing for family love. Journalists have berated her father for Forever Charlotte!, and seem sure she was exploited by a monster. But she is her father's child in more than just her social beliefs. She still won't listen to the radio, in case one of his songs breaks her heart.

Are family bonds important? "They are for me," she says, unreservedly.

She admits she loves acting, and it clearly touches deep feelings. So why, I try one last time, won't she talk about those feelings? Does she think to talk about them publicly would make them impure?

"Oh, that's much too profound," she says. "It's much more simple than that. I need things to be simple, because I'm very slow and square-minded. I don't pay attention to my feelings about my life when I'm shooting."

So if she never had to be interviewed, if she could just walk to the set and forget herself, then walk back to her quiet life, would she be happy?

"That's what happens," she says, laughing. "It's easy."

It could almost be true.