Above: Jacket, £125, Banana Republic; skirt, £140, French Connection; rings, £50 each, Thomas Sabo

“I worry about most of the decisions I make. I worry I have spoken too much at a dinner, I worry that I said something to a journalist that wouldn’t be understood in the right way. I worry about everything – it is a bit annoying really.”

Confessing that it’s only things that she can personally influence that bother her – “I worry way more in a car that I am driving than in a car that someone else is driving,” – she tells me how the futile phrase “Coulda, woulda, shoulda!” was banned in her house. “My sister once told me I was never allowed to tell her anything that started with I could, I should and I would.” It’s a mantra which helps her keep it under control.

She even worries about being controversial. Haunted by a comment she once made about regretting her appearance in Gossip Girl (2010) – “I wondered why I was there,” is what she’s believed to have said – Poésy refuses to set the record straight for fear of her words being taken out of context again. On reflection, the role of Chuck Bass’ European girlfriend Eva Coupeau does sit rather awkwardly on a CV that lists a string of French films alongside Danny Boyle’s 127 Hours (2010) and the television adaptation of Sebastian Faulks’ Birdsong (2012). And not counting the Harry Potter films, it’s the most mainstream thing she’s ever done – but she is not going to rake up that ground again today. “It was one of those weird interviews – I said something, it got taken… I just don’t talk about it anymore because it keeps coming back,” she tuts. “I just got really mad at the person who wrote that down.”

But even if Poésy is an habitual worrier, she knows how to use it to her advantage. “That is where humour comes in, otherwise it’s unbearable,” she says philosophically. “If you balance it with humour you are sort of OK.” And coming from a girl who was absolutely fine to wear a Russell & Bromley bag as a helmet, I really think she will be.

Clémence’s High-Street Hitlist

Whistles: “They’ve got really good leather.”

Acne: “You have to have a pair of jeans that aren’t falling apart.”

Topshop: “I always spend a few hours there as they have a good vintage section.”

The Tunnel starts Wednesday 16 October, 9pm on Sky Atlantic HD. The first episode will be available exclusively to Sky Customers through On Demand from Thursday 10 October

Clémence Poésy: strike a pose