Jessica Biel is not just a body. The 26-year-old actress is not just known for her fab abs, glutes, buttocks and breasts, and for boldly featuring them in movies such as The Rules of Attraction, Blade and Stealth. And, certainly, she’s not just a Hollywood poster girl, current partner of Justin Timberlake, and an über-babe. She’s more than that.

How much more? Well, for starters she goes head to head, and emerges unscathed, with national treasure Kristin Scott Thomas in the period comedy Easy Virtue. The film, adapted from an obscure Noel Coward play by Priscilla, Queen of the Desert director Stephan Elliot, details the effect that a brash young American wife Larita (Biel) has on the denizens of a crumbling English pile, and more specifically on her new mother-in-law, the terrifyingly respectable Veronica Whittaker (Thomas).

The two women trade barbs and slurs for 90 minutes in the midst of dinner parties and garden walks. A sample attack, from Thomas: “Is it true that you’ve had as many lovers as they say?” A sample retort, from Biel: “Of course it’s not true. Hardly any of them actually loved me.” And off-camera there was also frostiness.

“There was definitely an element of distance between us,” Biel admits. “Kristin would dip in and out of character. Mostly she stayed within a space that was kind of uncomfortable for me, but perfect for the film.” Director Elliot later adds: “Right from day one they were like cats circling each other. I said, ‘Don’t change a f***ing thing! Go with it!’ There’s a lot of reality coming off on this film."

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More importantly, the movie, which co-stars another treasure, Colin Firth, is never once compromised by Biel, an actress with, among others, Choctaw American Indian heritage who was once told that she was too “contemporary-looking” for period movies. On the contrary, she matches Firth and Thomas line for line, and proves herself a formidable screen force. “I knew that I was going to be judged,” she says. “I knew that I didn’t have the same training and background as Colin and Kristin, but I also knew I brought an interesting element, something different.”

Furthermore, Biel’s body, bar one slinky cocktail dress, is kept under wraps throughout. She suggests there might be a correlation between the amount of flesh that one exposes on screen and the perceived credibility of one’s performance, but warns that she won’t be adopting a cover-up policy any day soon. “Some actresses that I love have done plenty of nude scenes, like Julianne Moore. And that’s not trashy. It’s art. So it depends, really, on the projects.”

Biel is, she says, just a hometown girl who grew up in the shadow of the Rocky Mountains, in Boulder, Colorado. She says that she was an outdoor kid, a polite, passive and well-mannered daughter of an entrepreneur father and stay-at-home mother. An interest in musicals, however, dragged her towards the local stage and then to LA, where she won a Pringles commercial and subsequently a breakout role as preacher’s daughter Mary Camden in the long-running family-friendly series 7th Heaven.

Biel did little time in bit-part hell, and seemed to segue straight into leading roles in films such as Blade: Trinity and The Illusionist. Her star will rise further with a prestigious central performance in David O. Russell’s forthcoming Nailed. As the regularly snapped girlfriend of Timberlake, she’s aware that her anonymity is already gone for good. “It’s a tragic thing I can’t just walk out and get my mail in my pyjamas with a towel on my head, because it’s going to be all over a magazine if I do,” she says. She is tight-lipped about Timberlake (rumours abound that they are engaged, that she is pregnant, or both), and will only coyly admit that he visited the Easy Virtue set, and that being a good dancer is “just one of his many, many talents”.

Anyone who doubts her own talents, she says (megawatt smile on full beam), needs to just drop the whole body thing and look no further than Easy Virtue. “I want to send people to this movie and go, ‘See! I’m kind of serious! I can do it!’ ”

Easy Virtue shows at OWE2, Oct 28, 8.30pm and at Rich Mix, Oct 29, 8.45pm. General release: Nov 7

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