Keira Knightley: How the actress is confounding her critics

The star of 'Pirates of the Caribbean' and 'Pride & Prejudice' steps out of the shallows

"She walked into the audition room and oozed youthful vitality and confidence much like the character I wanted her to play. She was a delight to work with from start to finish and, from what I know, has remained very grounded, much like she was then," the writer-director Gurinder Chadha reflects on her first encounter with Keira Knightley, in the run-up to Bend It Like Beckham (2002), the film that made Knightley a star. It is only five years since Knightley, then 17, played Jules Paxton, the ebullient and instantly likeable player for the Hounslow Harriers. By her own admission, her performance wasn't especially polished. Although she had been acting since she was a child, she hadn't been to drama school.

Nonetheless, in the five years since, Knightley has turned into the most bankable young actor in Britain. This week, the 22-year-old has been in Venice for the world premiere of Joe Wright's Atonement, which is being touted as an Oscar contender, as well as the film that marks Knightley's coming of age as a serious actress.

Collaborators wax enthusiastic about Knightley's qualities on screen. "She really is a luminescent star," David Thompson, the head of BBC Films, says of her. "She is incredibly photogenic. She has that indefinable quality that makes the screen light up completely when she is on it. Of course, she is beautiful, but it is more than that. She has a lot of depth and she can really move an audience."

Like Gurinder Chadha, the Scottish director Gillies Mackinnon was instantly struck by her when she auditioned to play a teenage East End drug addict in his 2002 feature, Pure. At first glance, a pretty, demure young teenager from Teddington didn't seem the obvious choice to play a working-class junkie. She walked into the audition holding an art folder, clearly having come straight from school. The producers were sceptical about hiring such an ingénue but Mackinnon talked them round. "I just had a feeling she is going to be a star."

Pure hints at what makes Knightley such a distinctive actress. She has a sylph-like quality reminiscent of old silent stars like Lillian Gish or Mary Pickford, slender figures with blanched faces, high cheekbones and mournful eyes. She is beautiful but with a vulnerability. At the same time, she is lively and mischievous – an archetypal girl-next-door. Performing her party trick, playing "Raindrops Keep Falling On My Head" on her teeth, or telling anecdotes to American chat-show hosts, she appears approachable and funny. Wright originally shirked from casting her in Pride & Prejudice on the grounds that she was too beautiful. He saw her as an aloof and porcelain-like figure, but was relieved to discover that Knightley in person was "this incredibly vital, independent, scruffy-like person."

It helps, too, that she has been able to work so consistently. One obvious reason why Britain struggles to create movie stars is that so few films are made. Young actors appearing in a feature once every two or three years aren't able to learn to work with cameras. Knightley, however, has been able to learn on the job. Not all her credits have been especially distinguished, but she has been able to play everything from Jane Austen heroines to bad-ass action women (in Tony Scott's Domino.)

As the sociologist Leo Lowenthal observed, "the mythology of success contains two elements, hardships and breaks." Knightley's biography has both. Her mother, Sharman Macdonald, is a well-known playwright and her father, Will Knightley, is a stage actor and founder member of the Half Moon Theatre. At the time that Keira was born in 1985, they had one son (Caleb). Knightley told Macdonald they could only afford to have another child if she sold a script. At this point, Macdonald promptly won an Evening Standard Award for Most Promising Playwright.

By the time she made Bend It Like Beckham, Knightley already had a strong list of credits. She had appeared as Natalie Portman's handmaiden in Star Wars: The Phantom Menace at the age of 12, having announced at the age of three her decision to become an actress.

What directors seem to like about her is that she can be moulded. As Jacques Helleu, the artistic director of Chanel, put it in some surprisingly double-edged remarks after seeing Knightley in Pride & Prejudice: "Her natural flaws were visible... Keira wore no make-up. She wore lengths of fabric as dresses. She had almost no hairstyle, just a little bun behind her head."

As her popularity has grown, so – in certain quarters – has the resentment of her. She has become a cynosure for paparazzi and gossip columnists and Knightley is still not taken entirely seriously as an actress. She is unlikely to win many awards for playing Elizabeth Swann in the Pirates Of The Caribbean movies. Meanwhile, even in her more "serious" roles, she is sometimes treated as part of the decoration. Joe Wright doesn't hide his annoyance at the way her performance as Elizabeth Bennet in Pride & Prejudice was overlooked by the BAFTA voters (despite winning an Oscar nomination in the US). "It did sadden me that that was the case. I think she should have been nominated. Sometimes in Britain we're not very good at supporting each other," he says.

Knightley invariably strikes a phlegmatic note about her sudden and enormous celebrity. "If it all falls apart tomorrow, I have had a really nice run and so be it," she recently stated. "You can't expect the highs to last forever." There is a sense that she is currently engaged in a delicate and very difficult balancing act. Her fame has inevitably come at a cost. She was understandably furious at rumours that she was suffering from anorexia, and recently won a libel action against a British newspaper that suggested she had an eating disorder. She can't be comfortable, either, with the relentless poring over her private life. Knightley may want to live an ordinary, grounded life, telling chat-show hosts about her leaking washing machine and discussing her enthusiasm for Nigel Slater recipes or for cleaning out the fridge, but...

"Why would I want strangers to know me?" she asked in an interview with the Radio Times this week, going on to add that "the magic is in the screen, not knowing what is behind it." Such remarks can't help but appear either disingenuous or naive. The whole phenomenon of movie stardom is based on audiences having a knowledge – however incomplete and contrived by publicists – of their favourite actors.

Knightley is one of the few genuinely bankable British stars. She is versatile, too, with a universality of appeal. Kids like her. She is a pin-up for the lad's mag crowd. (FHM called her "the sexiest tomboy beanpole on the planet.") Thanks to costume dramas she is applauded by the older, more gentrified cinemagoers. Now, the critics are beginning to warm, realising that she brings depth and subtlety to her roles.

She has also begun to mix and match Hollywood studio projects with more adventurous – and less obviously commercial – independent titles. In The Edge Of Love, by BBC Films and nearing completion, she plays what promises to be her most provocative and risqué role: Vera Phillips, a former teenage sweetheart of the Welsh poet Dylan Thomas. Scripted by Knightley's mother, it reunites her with the film-maker John Maybury, who also directed her in The Jacket.

David Thompson believes that Atonement and The Edge Of Love will make audiences and critics reconsider Knightley. They will see that she is more than just a starlet who looks fetching on a pirate galleon. "She has an extraordinary range and a real capacity to plumb depths of pain and sorrow, as well as a lighter side to her. That is a rarity. Not many have this range of qualities."

'Atonement' is released on 7 September