Charlotte Gainsbourg is all skinny black jeans and understated grey T-shirt. She looks as if she’d be more at home in a café in Camden than here, in a glitzy cliff-top cabana at the Hotel du Cap in Antibes, overlooking a yacht-strewn stretch of the Med. Alongside some of the other guests strolling the lush grounds – the spray-tanned and surgically enhanced – she seems puritan pale and boyishly flat-chested, a willowy refugee from another time and place.

Still, conformity is not in Gainsbourg’s DNA. Now 37, Charlotte is the daughter of Jane Birkin and the late Serge Gainsbourg, the couple who famously incited a heady mix of moral disapproval and teenage thrill in 1969 with their gasping, sexually explicit song, Je t’aime... moi non plus. They went on to make a film together of the same name – he directed, she acted – in 1976, for which the UK censor refused a certificate. Charlotte was 5.

But times change. That film, whose sex scenes were once deemed so shocking, looks like an episode of Emmerdale compared with Charlotte Gainsbourg’s latest work, Antichrist. The day before our meeting, Antichrist – directed by Lars von Trier, one of contemporary cinema’s genuine auteurs or a crackpot misogynist, depending on whom you listen to – had screened at the Cannes Film Festival, a few miles down the road. Even among the hardened hacks and assembled movie industry types, who aren’t easily shocked, the film provoked extreme reactions and highly charged exchanges.

It’s easy to see why. Antichrist is the story of a couple, played by Gainsbourg and Dafoe, who struggle to cope with the devastating loss of their young son, who falls from a window in their apartment while they are making love. The couple retreat to a remote country cabin to work through their grief together. What follows is a descent into madness, a psychological horror with graphic, disturbing images designed to shock. Von Trier, who has suffered from chronic depression, says the film is “deeply personal”. If he’s dealing with his issues on film, then his therapist certainly has his or her work cut out.

There are scenes of graphic, joyless sexual coupling and brutal violence (at one point, Willem Dafoe, Gainsbourg’s co-star, is hit so hard in the groin he passes out). But the sequence that caused the most outrage was when Gainsbourg’s character – she is never given a name and in the script is referred to as “She” – mutilates her own genitals with a pair of scissors. At the press screening this provoked a cacophony of boos, hisses, some hysterical laughter and prompted half my row to look away in genuine horror. Quite a few headed for the exit, not to return. Later, at a press conference, one British journalist demanded that von Trier explain himself for putting an audience through such torture.

So why on earth would Gainsbourg want to take on such a role? “Because I don’t want to do obvious things and boring things. Yes, there was a lot of suffering and it was hard, but I’ve never lived something as strong. It was the most intense experience I’ve ever had.”

It must be noted, too, that Gainsbourg’s performance, which won her the best actress award at Cannes, is quite extraordinary. She knew, of course, that Antichrist was a cinematic time bomb from the moment she first read the script and was summoned to Copenhagen for an audition. Even so, she was still a little shaken by the reaction in Cannes.

“I didn’t think it would be as angry as that. People are affected by cinema, but that anger was something else. It was like being asked to justify a crime. It was very exaggerated.”

Sex scenes

Gainsbourg is polite and poised. Despite the difficulty of the subject matter, there are no embarrassing silences or pauses. She handles each question in the same even way, almost as though chatting about the weather, although the conversation ranges from on-screen masturbation to porn-star body doubles.

“Of course, there was the whole question of the nudity and the sex involved in this,” she says. “And all the graphic shots and being mixed with porn actors was something I had to agree to do. But it didn’t shock me. I was willing to do it. I’ve been quite reserved in the past and shy with my body, and with this film it was much stronger; it wasn’t just normal sex scenes. But I was totally with it and excited and thrilled by it. I don’t like what I see on screen, but it didn’t matter during the shoot. I was a bit shy about having no breasts at all, so I just told Lars that I was OK being naked and all of that, but it would be easier if I had a shirt on at times, even if I was naked below.

“So I had little difficulties, but we were able to deal with them. But mostly I forgot about myself; whether I was pretty or not pretty, if I had bags under my eyes and no make-up, or had spots everywhere… it had no importance. And no, I don’t think it was courageous of me. I just really wanted to work with Lars. I love his work and I’ve never been asked to go that far. As an actor, that’s what you hope for.”

Explore Film

• Film Reviews

• Trailers

• DVD

• London Film Festival

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010