Clémence Poésy: 'Making someone English laugh is one of the things I treasure most'

You're playing a French detective who works alongside British detective Karl Roebuck (Stephen Dillane) in new TV series The Tunnel, based on Scandinavian crime drama The Bridge. How does changing the nationalities alter the storyline?

Well, there's the language barrier between the French and English. We don't communicate well! But it's always interesting to explore borders and that point where you have to open up and discover something unknown, that's also so close to you. The writer of the show, Ben Richards, really wanted to explore aspects of society today that we often don't want to look at. Through the character of Karl, the English detective played by Stephen Dillane, Ben looks at his own parents' generation, their communist ideals and the battles they fought that their son didn't quite take on, and how that affects the world today.

Your character, Elise, is brilliant, but on the Asperger's spectrum. Was that hard to play?

Elise is very closed but pure like a kid who tells the truth all the time. She's as direct in her sex life. She just drives to a bar and picks up a man. She never lies and when you do that you get into a weird social space where you can't really have a relationship with anyone. Because we base most of our day-to-day chitchat on little lies; we pretend things are better than they are. But over the course of the series, she learns what it's like to let someone in.

Is it refreshing to have a male/female pairing that isn't about sex?

Yes. What I love about the show is it's truly about two people becoming friends. Elise turns into a pillar for Karl, the strong person he can hold on to. And you can see so much tenderness in his eyes for this strange little animal. With Stephen, it was amazing to work with someone so closely. We're not the same age, we're from different backgrounds, but I had his back and he had my back, which was a really happy thing. Not enough is written about friendship. So if we manage to [explore] that just a little bit – and not just a storyline about a serial killer – I'll be really happy.

You're often cast in very feminine roles. Was it a relief to be more of a tomboy?

Sometimes I watch TV shows and the female characters are supposed to be very strong and masculine and yet you can see the makeup has been expertly done. We decided not to have hair and makeup for Elise, apart from covering up shine and pimples. It does make her more real. What's disconcerting is when a journalist tells you: "This is really brave" and you think: "Oh my God, maybe it was just really stupid!"

With characters such as Carrie in Homeland and Hannah in Girls, we're seeing more complex roles for women, aren't we?

I find what's happening in the film and TV industry right now really fascinating. You don't have to be someone's girlfriend or wife or daughter. People such as Lena Dunham and Kristen Wiig are showing that a comedy with just women, produced by women, can be as successful as the ones with men. You don't have to look a certain way. You can speak your mind, be honest about what you go through as a woman. It's a really interesting way of taking feminism in a direction I love – lighter but still very involved.

Are you political?

I do define myself very clearly on the left – but I don't know if there's a party I would completely give myself to. But I've always tried not to let cynicism take over. Having the right to vote, and being able to choose who is governing you, is such an amazing privilege. I want to keep just the right amount of naivete and not get dragged into "it's all the same" because it's not. Feminism is a great word. I think as a woman you have a responsibility to say: "There are still fights to be had." Just look at what's happening in Texas right now [the controversial HB2 bill that severely restricts women's access to abortions is set to take effect in the state later this month]. I'm so glad my mum and my great-mum have fought those battles for me but I have to keep on doing it for the daughter I may have. There are parts of the world that are still medieval.

You've talked about feeling quite marginalised as a teenager. Do you have a strategy for dealing with bullies?

Like 80% of us, between 12 and 15 it was a bit difficult because I wasn't quite where I wanted to be. I didn't really try to fit in much. And I always thought: "I hope if I have a kid one day, I'll be able to spot it", because I didn't tell my parents I was going through something difficult. I think groups can be terrifying sometimes. They don't let you think on your own.

How did you recover?

I was lucky because I had the chance to go on an exchange programme to Toronto during those years. It was tough because [at my school] I wasn't one of the cool girls. But then I went to another school and all of a sudden because I was the new kid, I was popular. I realised how inconsistent it was – and how it didn't have anything to do with who I was. But I know exactly how heartbreaking [feeling marginalised] can be. So I started talking about it when Harry Potter came out [she played Fleur Delacour in three Potter films] because I knew the people reading the interviews might be kids going through that at school.

You made your Broadway debut in Cyrano de Bergerac as Roxane. Would you like to do more theatre?

I'm actually rehearsing a new one-woman play in Paris, directed by my father [Etienne Guichard], about a young girl in the Resistance. It's a little gem, I've wanted to do it for so long and I've had to turn down other jobs to do it. But I go to rehearsals every day and think: "God, I can't wait to do something with other people again!"

When are you setting up a French version of 5 x 15 soirees [where five people talk for 15 minutes each about a subject that they are passionate about]?

I've just done it in Paris with Camille Racine and my friend Sylvia who runs the Shakespeare and Company bookshop there. It's amazing. There's always someone new to discover; someone who makes you curious about a topic you never thought you'd be interested in.

Your English is fluent but do you ever find our sense of humour baffling?

Making someone English laugh is one of the things I treasure most. French seriousness can sometimes annoy me, although my mum and dad have a very fresh, funny way of looking at life. My mum has always said it's what makes life bearable. I share a sense of humour with all my closest friends, otherwise there's something missing. You can't really be friends.

The Tunnel starts on Sky Atlantic HD at 9pm on 16 October