Actress Clémence Poésy is the epitome of everything we Brits think of as French: classically, effortlessly chic and with that impossible-to-replicate aura of ‘cool’ about her. She’s a familiar and much-loved face in Britain, after her international breakthrough role in a little-known franchise called Harry Potter. She played Fleur Delacour, initially one of Harry’s competitors in an inter-school magic tournament and his later kick-ass sister-in-law.

As well as Potter, Poésy has starred alongside Colin Farrell and Potter co-star Brendan Gleeson as the Belgian criminal Chloë Villette in acclaimed 2008 dark comedy In Bruges. She also portrayed Rana, the lover of adventurer Aron Ralston (played by James Franco) in the six-time Oscar nominated 127 Hours in 2010.

Her part in Sky Atlantic’s 2013 hit The Tunnel (an Anglo-French remake of The Bridge) saw her heralded by critics for her performance as Elise Wasserman, the no-nonsense, eccentric partner to Stephen Dillane’s everyman Karl Roebuck. We sat down with Poésy at a recent press day in London to discuss the new series of The Tunnel over breakfast.

When we first met Elise, she was brilliant, coldly logical and unwilling to let others into her world. In season two, things have changed, Poésy says: “When we first start she’s just been promoted to a job that she didn’t really want. I think promotions often go with more administrative [work] and less of doing what you love [about] the job. I think she’s quite keen on trying to do a good job but she’s also not terribly enjoying that part of her job.”

“I think something maybe opened up in the first season – she’s a bit more curious, she’s a bit more ready to try a few things. She’s trying living with a boyfriend, she’s trying taking managerial courses, she’s trying a few things in her own way. I think deep down what’s happened is that she’s got a sense of guilt ever since what happened with Karl’s son [and] not having managed to avoid that. I think she’s probably pushed it down the way she does with emotions. She’s tried to put them aside and for

get it, but it’s there.”

While Elise and her Swedish counterpart Saga Norén (played by Sofia Helin) both possess traits that seem in line with Asperger Syndrome, Poésy says she does not portray the character with the belief she is on the autistic spectrum. Instead, “the way I approach her, and it was quite important in whole narrative of the first season anyway, is [through] her relationship to truth, which is incredibly raw and pure. She’s decided at some point in her life, because of something that happened to her, to just look at facts and tell the truth and not worry about anything else. To be honest, if you look at life like that, everything changes. If we all just said the truth we’d be completely different.”

There is a much-quoted interview that Poésy gave after the first season of The Tunnel, where she admitted her grandmother enjoyed watching the series but commented that Poésy should find “nicer” characters to portray. Asked if she likes the character of Elise, despite her not being “likeable”, Poésy immediately jokes: “What are you talking about?”

“I see her as really pure and fragile – for me she’s kind of like a kid almost and I find her really moving. I don’t think you have to like a character or love a character, but you have to lose judgement to play them.”

Most of the reason she was attracted to the initial script for The Tunnel was the relationship between Elise and Stephen Dillane’s British detective Karl, she reveals: “I think it’s quite rare to talk about a male female friendship that is actually just friendship and doesn’t end up a seduction game.”

Indeed, their relationship is both engaging and heartwarming – despite the lack of the sexual connection so often seen on television between opposite gender leads. Has being part of big franchises, such as Harry Potter and Game of Thrones, helped their chemistry? Poésy bursts out laughing, confessing: “It’s something we’ve never talked about.”

What is the secret to their on-screen chemistry then? “It just comes from spending a lot of time together and working together and him being an incredible actor and an amazing man to work with. On a series, you have to be a team more than on a film. On a film you’re on a trip with the director, it’s his film, you know how it ends, you’re in the story of this man. With a series, you’re much more responsible for your characters, because directors change all the time and you’re not entirely sure how the series actually ends. The constant is you and your partners.”

Our conversation turns to Britain and the oncoming EU referendum, which Poésy fears may make both her personal (she splits her time equally between London and Paris) and her professional life (The Tunnel is an Anglo-French production) more difficult. However, what she will miss the most should #Brexit occur is the idealistic beauty of a European Union: “I was brought up with the idea of a European dream, and this idea that it was made possible. As complicated as it is, and as problematic as it is, and as economically tricky as it is, the idea of it I think is such a strong and beautiful thing. I love England so much that I’d really miss it.”

On the topic of her homeland, we ask whether the French – as famed film lovers – have softened towards television in recent years. Poésy thinks yes, largely due to the release of highly successful French zombie drama The Returned. On her own transition into television, Poésy says: “I think if that hadn’t happened I wouldn’t have wanted to do something, but The Returned did change the whole way TV was looked at. And now, every new series [Canal+] have, you want to be a part of. It was kind of meant to happen anyway, because American TV was so good, English TV was so good, they had to at some point catch up.”

The Tunnel: Sabotage is available from 12th April 9pm on Sky Atlantic, with all episodes available same night via Sky Box Sets.