Carey Mulligan's in a class of her own

Just under a year ago, Carey Mulligan was sleeping quite soundly at night. Then she found out An Education was going to play at the Sundance Film Festival. The weight of shouldering her first lead suddenly hit her. "I started freaking out that if everybody hated it, it would be all my fault," she explains. "I had these anxiety dreams – very basic anxiety dreams – where Geoff Gilmore, the [former] director of Sundance put me in a car and made me leave for being disappointing. In Park City, in the main high street, he gets this black car and he's like, 'Get in. You've got to go. Everyone thought it was going to be really good!'"

Fortunately, everybody did think it was good. Better than good, as it goes. Winner of the Audience Award, An Education has since become one of the most talked-about films this year. What's more, the London-born Mulligan has become the centre of attention for her breakthrough role as Jenny, a 16-year-old schoolgirl who falls under the spell of an older man (Peter Sarsgaard) in 1960s suburban England. Already nominated for a British Independent Film Award for Best Actress, an Oscar nod is now a very real possibility (Ladbroke's make her second favourite at 5-1 to win Best Actress, behind Meryl Streep for Julie & Julia). No wonder Time magazine recently proclaimed, "Carey Mulligan: a star is born".

For once, this is not hyperbole. With a host of high-profile Hollywood projects to hit screens in the next year, Mulligan has just finished shooting Wall Street 2: Money Never Sleeps, Oliver Stone's sequel to his 1987 corporate classic Wall Street, in which she plays the coveted role of Winnie, daughter to Michael Douglas's fresh-out-of-prison Gordon Gekko. From that, she's moved straight on to the latest screen adaptation of Graham Greene's Brighton Rock, alongside Sam Riley, Andrea Riseborough and Helen Mirren. The fact that Mulligan once secretly applied to three drama schools on her Ucas form, only to be rejected by all of them, now must seem like light years ago.

Not that Mulligan is one to gloat. "It doesn't feel like anything massive has changed," she tells me, in between scooping spoonfuls of yoghurt into her mouth. In person, she's polite, modest and self-deprecating. She practically melts when the subject of Nick Hornby, who adapted journalist Lynn Barber's memoirs into An Education, is raised. "He's so much more interesting than I am," she coos. Despite a decent run at the BBC – everything from Bleak House to playing Sally Sparrow in the much-feted Dr Who episode "Blink" – An Education is the first time Mulligan has done publicity. "I never wanted to do it until I was really proud of something. I don't like the idea of self-promotion."

This, of course, may change – not least because Hollywood studios, being what they are, noticed her long ago. Earlier this year, she was seen in a brief (and – with a peroxide cut – almost unrecognisable) role opposite Johnny Depp as one of John Dillinger's regular prostitutes in Michael Mann's gangster film Public Enemies. Before that, she completed The Greatest, alongside Pierce Brosnan and Susan Sarandon, which also bowed in Sundance when An Education did. "It's about a family who lose their son," she explains. She plays the pregnant girlfriend of the boy who dies. Early reviews were largely positive, with Mulligan bringing a "bracing resilience" to the role.

In the UK, however, she will next be seen alongside Jake Gyllenhaal, Tobey Maguire and Natalie Portman in Jim Sheridan's Brothers. A US remake of the Danish film by Susanne Bier, it's been in post-production for some time. Mulligan notes "it feels like a million years ago" since she made it. She plays the wife of a soldier accidentally killed by Maguire's character. "It's a small part but Jim's very playful, and he slotted me into lots of the rest of the movie. We improvised that scene more than it was written. He's such an amazing film-maker. I want to work with him and play a bigger part, if I'm lucky enough, because he's so amazing. In America is one of my favourite movies."

By anyone's standards, Mulligan's rise over the past year has been remarkable. "It's unusual that you can become so famous at such speed," says director Lone Scherfig, who can no doubt take some credit for her success after casting her in An Education. "All these films she hadn't done when we were shooting. She got these parts because the agent took some of our footage and showed it. So she is an unusual talent because of course there's a reason why all these American directors would even want her in films where she has to play American. They acknowledge that she has got something that's not that common. First of all, she can carry a film. It's not just carrying a role. She's poised and elegant and has a beautiful voice and a beautiful dialect. She's very intelligent – which is also helpful."

Inevitably, the rush to anoint her as "the new..." has begun in earnest. Trade paper Variety kicked off proceedings, after observing of the scene in An Education where Jenny goes to Paris that "you could almost swear you're watching Audrey Hepburn skipping through the same streets 50 years ago". Indeed, with her brunette crop and mischievous smile, you now can't read a Mulligan article without seeing the word "gamine" in front of her name. Then of course there are the inevitable Keira Knightley comparisons. The pair first met on Mulligan's first film, Joe Wright's 2005 adaptation Pride & Prejudice, in which she played Kitty Bennett, sister to Knightley's Elizabeth.

Since then, they've become firm friends – and recently reunited for Mark Romanek's adaptation of Kazuo Ishiguro's novel Never Let Me Go, yet another high-profile project Mulligan has for 2010. Does she see Knightley as a role model, I wonder? "Yes. She's done bigger films than I have done. Obviously – she's massively famous. But, yeah, she is. She has a lot of bad stuff to deal with. She gets a really hard time from the press sometimes, and she deals with it really gracefully. Also, she's one of my best friends, so it's hard to talk about her really. We're really close. Keira and I are very tight." In truth, while Mulligan may not survive the Hepburn comparison (but then no one ever has), she certainly has the talent to eclipse Knightley as Britain's brightest young actress.

Her early years have evidently already prepared her for the extraordinary life she's now living. Now retired, her father used to run the European arm of Intercontinental Hotels – which meant Mulligan and her brother Owen spent their early years at the International School of Düsseldorf. Her sibling was the first to start acting, in a school production of The King and I. "This story makes me sound like a precocious brat!" she laughs. "He was on stage and I was watching. And I started crying because I was too young to be in it, and they said, 'OK, fine, you can do it because you're Owen's younger sister.' And they put me in it. And from then on, it's all I've ever wanted to do."

After boarding at a Rudolf Steiner school, Mulligan got her big break after writing a letter to Julian Fellowes, the Oscar-winning screenwriter of Gosford Park. Inviting her to lunch, he then introduced her to a casting agent who put her forward for Pride & Prejudice. Joe Wright remembers when he first met her. "She was this 18-year-old who was working in a pub and had dreams of being an actor. She came in, and she was really good in the casting session, so we gave her the job. She used to walk on to every set and start crying – 'It's so beautiful!'"

Mulligan herself can recall what she was like in her early days. "I was just quite shy," she says. "I didn't really have a proper relationship until I was 19. I was kind of a loser." Then she did Pride & Prejudice and something shifted. "I fell in love with everybody on that film. I was in love with Rupert Friend for like a month. He's one of my good friends now. It was like, 'Oh, boys! You, you, you and you' – the boom, the sound guy, lighting, yes, everyone. I'd not really been around! I didn't end up with any of them. I had very romantic crushes. Being on a film set was mad."

This year, she started dating her Wall Street 2 co-star Shia LaBeouf, a further indication that Hollywood has begun to embrace her as one of its own. While she recently admitted that she's still considering going to acting school, after walking past Julliard in New York, in reality the chances are slim when studios are clamouring for her. She's all too aware that this is her time – to the point where she doesn't want to continue with her favourite pastime. "I get more nervous of going ski-ing now," she says. "I don't want to go and break a leg and lose a job. So more walking now."

If this suggests she's become more conscious of the position she's suddenly been elevated to in her profession, Mulligan thankfully still speaks about the industry with wide-eyed enthusiasm. Such as the moment she talks about working with a "reduced crew" on the Paris scenes for An Education before immediately flying to Chicago to the vast studio-backed set of Public Enemies. "There were 300 extras!" she gasps. "All dressed in Thirties gear. Fifty actual vehicles! Catering tents. Craft services is mind-blowingly exciting for me. The food in America is so much better than it is in England. It was mad. It was a completely different experience."

While this may be put down to youthful exuberance, Mulligan is also capable of cool self-analysis, as she shows when asked to compare herself to her character in An Education. "At that age, I wasn't as interesting as she is. What I love about her is that she is so fascinated by everything. She has such a thirst for knowledge and I didn't have that. And still don't have it as much as she does. She really is interested in 17 different things at once, and is massively enthusiastic about art, music and culture. So, no, I wasn't like that. I was much more basic." Admittedly, "basic" is not a word that fits her any more. Not only has a star been born – but one whose career looks to have a longevity few starlets ever achieve. Might be worth getting down to Ladbrokes and placing that Oscar bet.

'An Education' is on general release. 'Brothers' opens on 22 January 2010