The actor and singer has long wrestled with the taboo-tackling legacy of her father Serge’s songwriting. But as her new album Rest is released, has she finally found her confidence? And what does she make of the allegations against her Nymphomaniac director?

When she was 19, Charlotte Gainsbourg saw a news flash on the TV saying her father was dead. Firemen were breaking into Serge Gainsbourg’s house on Rue de Verneuil, near the hotel where we meet. After his death, Gainsbourg, her stepmother Bambou and half-sister Kate Barry lay next to his body as well-wishers visited. “We were like dogs around him,” she says. “It was a weird few days – it felt like a week. I didn’t want to let go. So, I stayed until I couldn’t.”

She laughs, surprisingly. It’s easy to see Gainsbourg as fragile. Wearing jeans, a vest, and a Le Smoking jacket, the 46-year-old singer and actor seems slim enough to fold up. She whispers to waiters. It’s hard to imagine her listening to Post Malone and Cardi B, her brash current favourites. But she’s upbeat, despite just arriving from New York – unemotional and enthusiastic, even when discussing her father, and Barry, who died almost four years ago in an assumed suicide.

Gainsbourg’s gorgeous new album, Rest – muted disco with a tumultuous undercurrent – explores these tragedies. It’s her fourth record, but first as lyricist. Her devoted father wrote her debut, 1986’s Charlotte for Ever. Air produced 2006’s dreamy 5:55, with Jarvis Cocker and Neil Hannon on lyrics; Beck masterminded 2009’s freewheeling IRM. Gainsbourg was always insecure about writing, especially in French due to her father’s legacy. But after an impromptu retreat with psychedelic New Zealander Connan Mockasin, “I saw that I was able to write things. But I wasn’t proud of myself.”

She had started writing before Barry’s death, including the brutal Lying With You, about her father’s body. She sings in French about his waxen face and the unforgettable sound of coffin nails. She couldn’t talk about him for years. “It was so violent not to be able to go through something intimately and without people looking into my life. But, of course, my father was public, so I had to share.” She smiles. “This idea of not wanting to share, that was the song. I had wanted to say that for a long time.”

Facebook Twitter Pinterest Charlotte Gainsbourg performing at Somerset House, London, in 2012. Photograph: Joseph Okpako/WireImage

Twenty-six years later, she still tries to avoid seeing photos of him or hearing his music. But when she lost her sister, all she could do was talk and write about her. “It was the complete opposite. Two different ways of grieving, but it’s never over.” Four years later, she can decide whether grief “still destroys me or not. I can choose the moments. It’s not something that’s imposed as much.”

Gainsbourg, her partner, the actor Yvan Attal, and their three kids tried to stay in Paris after Barry’s death – she didn’t know if she would survive. “Kate was always fragile, but I was the one she was protecting. We always thought we would be two old ladies in the same house. That was our life raft. I had to decide that I wanted to live. And that I really wanted to live for my children, and I wanted to get better. And that’s why, selfishly, I ran away.” The family fled to New York. “Drawing and taking pictures and discovering this city” became Gainsbourg’s coping mechanisms. She has sketches on her phone: tender, orange drawings of her daughters; harsh, black self-portraits. “Everything was new, so it was very refreshing. It didn’t mean I forgot about Kate’s death, but it was less real.”

She had tried to start making her fourth record in Paris with producer Sebastian Akchoté. He turned up to their first meeting wasted, issuing orders “in a sort of paternalistic way”. But she found him charming. After some false starts, he came to New York and gave Gainsbourg’s melancholy lyrics their violent musical “shield”. She hired professional songwriters to refine her words, but rejected their changes. “It was not me any more. I realised that I like my imperfections.” The featherlight Les Oxalis was initially an erotic fantasy before Gainsbourg decided to rewrite it to depict her sister’s grave. “Not sexy at all! Sebastian was always excited by the music and lyrics being in opposition, but for this he said, are you sure you won’t feel uncomfortable singing these words over a disco energy? But I was completely sure that was the only way.” Paul McCartney, Owen Pallett and Daft Punk’s Guy Manuel de Homem-Christo all pop up at points.

Even the songs that aren’t about death are disquieting. On Dans Vos Airs, Gainsbourg looks at her children and fears the passing of time, a constant preoccupation. “I don’t feel life is beautiful and all that, I don’t,” she says, still upbeat. Weathering terrible losses doesn’t make the future less scary. “You’re conditioned to be scared every time the telephone rings.” Ageing also holds little appeal. She worries about great film roles drying up. But then she loved transforming into a 70-year-old for her latest film, La Promesse de l’Aube. The wizened reflection felt prophetic. “I won’t be like my mother, I’ll be like my father, as a girl, which is not that nice. But I know I’m taking his looks.”

Gainsbourg wants to make a documentary about her mother, Jane Birkin, and shot footage when she played Japan this August, “an excuse to get close to her. But also to show her that I cared so much.” Gainsbourg’s childhood adoration of her father is crystallised in pop infamy. Released in 1984, when she was 12, their duet Lemon Incest laments “the love that we will never make together”. After her parents split, when she was nine, her relationship with her mother was more prosaic. Time with Serge was “precious, it wasn’t real life. My mother had the real life.” At home, Gainsbourg hid in her room watching the phone. “And I just lived for that phone call.” Aged 15 to 19, Gainsbourg dated an older man, who only met her parents once “to swear that nothing was going on”. She laughs, and won’t reveal his age or how they met. “Ooh, big age difference,” she teases. She doesn’t feel he took advantage. “I don’t feel that it was wrong. I should, but I don’t.”

She was a shy, obedient daughter, yet determined to create something for herself, starting her film career age 12. In interviews from the period, she looks as if she would rather have teeth pulled than appear in public. She doesn’t understand why she did it. “My mother left a note saying, ‘If you want to go to the casting for [her first film] Paroles et Musique, here’s the address.’ If I went, it meant I wanted something to happen. And I remember being thrilled when I got chosen.”

Facebook Twitter Pinterest Jane Birkin and Serge Gainsbourg with Charlotte in 1971. Photograph: Alamy Stock Photo

These contradictions underpin Gainsbourg’s intrigue: the shy girl who didn’t just want to act, but picked transgressive roles. She loved the provocative Lemon Incest, and 1986’s equally ambiguous Charlotte for Ever – her father’s film that accompanied her album. Age 22, she starred in her uncle Andrew Birkin’s film The Cement Garden, about incestuous siblings. Director Lars von Trier provided her most notorious recent roles. “I find it interesting to put myself in those positions – in Nymphomaniac to go into those weird grounds of masochism. I enjoyed myself, a lot. So, I did ask myself, maybe I am masochistic? I must have a streak. I don’t like real-life violence. But there’s something that I find … tempting, I guess. I don’t want to analyse it too much.”

She read Björk’s allegations that the Danish director sexually harassed her (claims Von Trier denies) on the set of 2000’s Dancer in the Dark. “Well, yes, maybe he’s capable of that. But he didn’t do it with me. And I never felt that he was forcing me into anything, so I don’t feel it’s doing him justice. But then maybe he was that way with her, I can’t say.” The boundaries on their collaborations were detailed in explicit contracts. Only once did she pull out of a scene, in Antichrist, where her character mashes a man’s penis with a log.

She understands why people might suspect these experiences post-Weinstein. “I find it so shocking today to see all these women come out with tragedies that were forced on them. That’s what I find terrifying.” She makes a clear distinction with her punishing roles. “I’m totally volontaire. With acting, you’re in a seduction mode, we all know that. You’re not a vulnerable actress going into a producer’s bedroom.” She’s never been in that position. “But I’ve played with my charm, of course. That’s the whole point. And it goes both ways. But it’s the equilibre of power that I find so terrifying today, the war of power.”

We gawp at the news that Harvey Weinstein hired ex-Mossad spies to suppress allegations against him. “So of course, there’s this power and this whole intelligentsia behind it that participates. I don’t like the sort of feminist streak, you know, the too loud – but I think it’s wonderful that it’s finally happening.”

What does she mean, feminist streak? “I don’t like it when it becomes an extreme. You know, if feminism means against men, I don’t like that.”

I assure her that nobody thinks that, bar men’s rights activists. Does she find the #MeToo movement extreme? “No, no, no. I think it’s wonderful that finally it’s happening everywhere – not only films, not only politics. And that’s good.” She demurs at embracing the word “feminist”. “I don’t know what I am. I’ll defend women, and I feel very, very – yeah, in the same boat.”

No artist today could pull off her father’s provocations, not limited to: a concept album about Nazis, saying he wanted “to fuck” Whitney Houston on TV while she sat next to him, or the whole incest thing. But is anything lost when these grey areas become black and white? Gainsbourg sighs. “I find it so difficult to answer. I want to say how good it was to be able to be in that provocation, to express shocking things but have a game with it. Today it seems that you can’t talk about anything. Everything is suspect. Everything makes people uncomfortable, or it’s too shocking. I regret that. And at the same time, when women have been mistreated, and real harm has been done, then you can’t really mess around and have fun.” She describes 2017 as “a very extremist era. And I hate extremes.”

Gainsbourg is more confident than she used to be. On I’m a Lie, she expresses the frustrations of shyness so brutally that they become hilarious – only a confident person could sing, “I drink my embarrassment from the toilet bowl.” And not wanting to sing in French because of her father implies fear, but also a reluctance to bother unless she could better him. “Exactly! I’ve always felt that ambitious because I judge myself, and it’s never good enough. It’s not a negative feeling. It’s just giving me an excitement for next time.”

She wasn’t going to tour Rest. But now she’s rehearsing in New York, emboldened by the personal boundaries she has broken so far. “Until now I was always pretending to be capable of doing it. And it was always a question of: will people see how uncomfortable I am? Now I don’t care. I don’t want to pretend that I’m comfortable, that I have a big voice. And it’s not that it’s suddenly that I feel it’s enough. It’s just that that’s who I am.” Finally, Gainsbourg says, she feels proud. It doesn’t happen very often.

Rest is released on 17 November on Because