Sagnier, whose English flows throaty and cognac-rich, leaves the words hanging in the air like the smoke from her cigarette. When searching for a word, three rapid yehs — and it’s not yeah — regularly punctuate her sentences. “I also had to diet and lose eight kilos, which was very bad,” she adds with a frown. “I like to eat and drink.”

There comes a point, pretty quickly, in every interview when it becomes plain that it’s either going to be an enjoyable experience or one to bring to an end as swiftly and painlessly as possible. With Sagnier, over black coffee in a Parisian cafe, it is writ as large as the Eiffel Tower: this gal is good fun. We’re not here to discuss sex at all (though more on this later), but to chat about her latest role in a new, big-budget film version of Peter Pan. She plays Tinker Bell, surely as far away from Julie, the young sexual predator in Swimming Pool, as it’s possible to be. She wears wings and a ballet-like skirt made of leaves, and stands about 3in high to 14-year-old Jeremy Sumpter’s Peter, in what is the first straight screen version of the original JM Barrie stage show.

Peter Pan’s director, PJ Hogan, who can count Muriel’s Wedding and My Best Friend’s Wedding among past successes, was instantly smitten by his Tinker Bell. He had trawled through auditions in America, Australia and Britain before finally taking in Paris. “He did not want Tinker Bell to be too girlie,” Sagnier recalls. “He wanted me to be a little clown. So I had this idea for the audition of sitting and pulling about 100 faces. I was not afraid of being ridiculous. He said: ‘You are the Frenchiest Tinker Bell I have ever seen — you are hired.’”

But Tinker Bell does not actually speak, and with much computer-generated work required, she found herself hanging in front of a blue or green screen in a vast studio near Brisbane for the re-creation of Neverland. “I had no lines, no partner and I spent much time on wires,” she reports. “It was all very technical. I just got on with it and thought childlike thoughts.”

Such thinking did not help when the director decided to bond the characters by giving Sagnier and Sumpter some time together in the Queensland countryside, without much of an introduction. “Jeremy thought I was his age,” she says. “When he saw me smoking, he said: ‘Oh, no, does your momma know?’ He is from Kentucky and speaks like that. I thought: ‘That is an odd thing to say.’ Then his mother took me to one side and said: ‘He is starting to fall in love with you. Tell him the truth about your age, otherwise it is going to be a bit of a problem.’ So I broke the poor boy’s heart. He was so disappointed and shocked. Then he seemed to fall in love with Wendy (the English child actress Rachel Hurd-Wood), who was the same age. That was much better.”

Sagnier is equally unguarded about her thoughts on child stars in general. “I always fear for them,” she says. “I’m a bit worried for Jeremy. He does not know anything about life, yet he’s suddenly going to have millions of fans. He will think he is the centre of the universe. He now lives in LA — which already thinks it’s the centre of the universe.” She visited the city for the first time in the wake of Swimming Pool’s American launch. Viewed from where we now sit, with red wine being served in small tumblers and the air thick with Gauloises, it seems slightly less fun than a clinic.

“Cinema is a war in Hollywood,” says Sagnier, with obvious distaste. “You have to be like a trooper. If you are not ambitious to the death, you are going to find it difficult. It is so different here in Europe. When I returned from California, I came back with British Airways to change flights in London. When I saw the River Thames from the window, I thought: ‘Home.’ When I was back in England, I felt happy. Nobody wants to cut your throat to get a part in England or France. We think differently to America.”

Those thought processes were remarkably unanimous, though, when the blonde, blue-eyed, all-woman Sagnier was seen in Swimming Pool, disturbing her rather starchy landlady, Charlotte Rampling, at every turn. This is why she has scripts piled high in her loft apartment, most of them American. “The fuss was a bit too much,” she reflects. “I had been doing little French movies before, yet suddenly I was getting the same level of exposure as Nicole Kidman.”

Her on-screen exposure was no less comfortable. “The first time my character is supposed to have sex, it is on a couch,” she recalls. “Charlotte is looking at us, and I was shy to do this in front of her. This particular actor was quite rough, for some reason, and the scene did not work at all between us. The day before, I had been swimming, and had cracked my nose on the wall of the pool. With the nose hurting, the guy kissing violently and Charlotte watching... it was surreal.

He was suggesting all sorts of things to the director. I would be saying: ‘No, thank you.’ It was all too much for me.” It became too much for her regular boyfriend, too. She decided to dump him before filming — and picked up their relationship only after it was over. “I was too absorbed in my character, and needed to be single to film those scenes. I went back to him six months later.”

There was no such problem playing little Tinker Bell. But whether Sagnier will be shining her light in Hollywood soon is open to question. “Los Angeles is all so... yeh, yeh, yeh,” she says. “I do not get manicures every day, I don’t dye my hair, I don’t bleach my teeth, I do not do diets. Do they need me?” Probably more than she needs them, that’s for sure.

Peter Pan is released on Boxing Day

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