'His underpants, of course, were the first things I asked for,' says Keira Knightley of her latest co-star, the legendarily attractive actor Johnny Depp. A slight figure in scuffed, schoolgirl jeans, smudgy trainers, with black beanie squished down, she seems normal and inconspicuous as she shunts down into the restaurant chair. No one notices her. This is not the usual incarnation of Keira Knighley, whose luminous screen presence has landed her this summer's major female lead in the swashbuckling $150 million epic Pirates of the Caribbean. And then there's working with Johnny Depp. 'my friends begged me for his pants, autographs empty bottles, cigarette butts - anything eBay would take. They'd camped outside Richmond Theatre when he was filming there. It took me about two weeks to break the news that I would be working with him.'

You don't see what everyone's been banging on about immediately (the beanie stays on, obscuring her features), but suddenly you realise her skin is as flawless as a Canova bust. She's an unexpected nutmeg brown from six months spent filming in the Caribbean and Los Angeles - a far cry from her milky radiance as Lara in the TV series Doctor Zhivago (which she hasn't seen yet because she was away). Nevertheless, she had her first experience of being nobbled by a fan only a few days ago.

'A woman ran over to me on the bus and started reeling off all the stuff I'd done. I felt like a real failure for being on the bus and not in a stretch limo,' she says, smiling. She orders a sparrow- sized starter and, more enthusiastically, a glass of white wine - it's only a week after her 18th birthday and she says she's making the most of it as. of course. she's 'never had a drink before in her life'.

'To tell the truth, I wasn't a Johnny Depp girl beforehand,' she says of Pirates. "More a Leo DiCaprio fan. But now...' she nods vigorously, I'm a Johnny Depp girl. He's the of the most intelligent, totally chilled out.' She burbles on, her conversation peppered with 'dude' and 'wicked'. But it's got Depp whom she'll be smooching with in Pirates; it's fellow Brit and ex-elf Orlando Bloom. The verdict?

'Can't you tell from how good-looking he is?' she laughs. 'Yes, he's very, very, very good indeed.' She recovers her modesty. 'Well, not quite the best in the world, but damn good. Nothing to be ashamed of.'

She's personable, even scarily confident. I In fact, Knightley is slightly freaky - like I some genetically enhanced strawberry - completely outgrowing people's expectations well before her time. Her conversation glides easily from football to Agent Provocateur underwear (given to her by a girlfriend) to hearty, devil-may-care descriptions of various auditions in front of the titans of the film industry.

'My Pirates audition was in Chelsea and I arrived half an hour late,' she says. 'I was sweating like a pig -1 thought I'd totally messed it up, but the next day the casting agent telephoned to say everyone loved me. I had to go out immediately to see Gore Verbinski [director of The Mexican and The Ring], then I was whisked to New York to see Jerry Bruckheimer [producer of Con Air, Black Hawk Down, Pearl Harbour and Armageddon], all in four days.'

Together with Rosamund Pike, Sophia Myles and Romola Garai, Knightley is one of the female 'hopes' of British cinema. But unlike those two, she has been in the acting business for a long time. She started getting bit-parts - 'niece of so-and-so, little sisters' - at the age of seven, through her parents. Her mother, Sharman MacDonald, is a playwright and novelist and her father, Will Knightley, is an actor. It is said that she asked for an agent at the tender age of three, because she felt left out with everyone around her ringing them.

Keira grew up in Teddington, Middlesex, in a 'very liberal' household, along with an older brother, Caleb, who is in computers but 'on the music side of things', and helps out as a teacher at a youth club. Her upbringing has instilled a certain worthiness in her, but she doesn't make an issue of it. She talks convincingly, and unbrattishly, about the value of education, how she admires Sean Penn for his political honesty and, when asked what her ideal role would be, comes out with, 'Eleanor of Aquitaine in The Lion In Winter' without missing a beat. She is obsessed by Eleanor, and by Josephine Bonaparte.

She lifts up her voluminous dog-eared bag and empties it out onto the table, revealing contents far removed from the usual actressy paraphernalia of Evian and lipgloss: two scripts, two books and an audiotape of Margaret Atwood's The Blind Assassin.

I'm not sure if it's the schoolgirlie bag, her sparkly purse (one of the few things she saved when she found herself on a sinking ship returning from the Pirates set), her fondness for grungy clothes, or the fact that her mother was with her for filming in the Caribbean, but Knightley is, thank God, unsophisticated around the edges. After all, it's only a couple of years since she left her A-levels and the comp in Teddington -which she 'loved and hated' - to pursue her acting career. Since then, she's appeared in films such as the arthouse thriller The Hole and Bend It Like Beckham, which is currently enjoying unexpected success in the US.

But what sets Knightley apart from her gum-chewing, Topshop-enslaved peers is an uncommon mixture of worldliness and ability, perhaps nourished by the careers of her parents, and all firmly underscored by ambition. She admits to being ambitious - how could such a wunderkind not? - but doesn't like the word because it is so easily mixed up with ruthlessness, and she doesn't think she's ruthless. It's just that she likes success - but at the same time is fully ready to chat about her shortcomings.

'I'm terrified that I can only play one type,' she says of her acting ability. 'If I was acting and barely mediocre, that would be awful.' She hasn't tried stage acting yet, but knows that's a real tester and has marked it down as something she must attempt before too long. She's got 'all the normal insecurities -the image ones, spots, thunder thighs. I have occasionally tried the gym but it gets to the point where it really doesn't feel good and you go an unnatural colour, so I stopped.' She thinks Kate Winslet is an excellent role model, fancied Viggo Mortensen in The Lord of the Rings, got shamelessly drunk on her 18th birthday and paints a lot in her spare time 'very badly'.

The big question now is what Hollywood will offer after Pirates. She felt that LA was a lonely place, and often found herself retreating with Bloom to a local English pub 'to watch footie, have a fried breakfast and PG Tips'; and these vague feelings of homesickness have persuaded her that, for the moment at least, Hollywood isn't for her. So, what's the contingency plan in the unlikely event of acting not working out?

'I could become a princess, I suppose,' she says. 'Marry William or Harry - there are two of them, aren't there? But you get to be a range of things when you're acting -princess one day, tramp the next.'

Tatler magazine - June 03