LONDON Maybe it`s because we normally see her in pretty dresses and bonnets, speaking so exquisitely crisply, that it feels strange, paradoxical even, to be sworn at by Keira

Knightley. Like a spurt of cheap lager from a fine Wedgwood teapot. Can she really have just told me to get lost? When all I asked was who she went on holiday with?

Knightley has a new film out, about which more later. We are sitting in a posh London hotel where she drinks green tea, and sits, like a cat, in the middle of an impossibly plumped-up sofa cushion. There is something quite feline about Knightley. When we talk about her work, she purrs. No, not literally - that would be weird — but she speaks easily, and appears content and relaxed. When I attempt to steer the conversation towards her life outside work, the claws come out. In a very good-natured, playful way, it has to be said. At times the interview feels like a sparring match, and she gives as good as she gets, if not better. She`s very entertaining company, and it`s fun - trying to get under the guard of Keira Knightley.

This will sound like the tragic fantasy of a male journalist who has fallen under the spell of a very pretty young lady and somehow imagines he could be her friend, but although she does speak awful proper, there is something nicely un-starry about her. Perhaps it`s being sworn at, but I`m finding it hard to remember that I am talking to the second highest-paid actress in Hollywood last year, although there seems be some debate about exactly how much she made.

“According to Forbes magazine, I earned 32 million last year,” she says, though she can`t remember if it`s dollars or pounds (it`s dollars).

Is that not true? “Unfortunately, no.”

How much did you earn? “Get lost.”

She says that money is not important beyond being comfortable, that she owns her own flat “somewhere in London”, and she mentions a new sofa. When I ask how much the sofa was, I get the inevitable (and probably well-deserved) “get lost”.

She doesn`t want to talk about politics much, because she doesn`t feel confident talking about it, though when I ask what she votes, she says, “My dad was a founder member of a leftwing theatre company, I went to a comprehensive - what do you think?”

Her father is an actor, her mother is a playwright, and young Keira was brought up in Teddington, west London. How posh does that make her, I wonder. “Why are you so obsessed with poshness? Somebody from the Observer asked me why I don`t have a cockney accent, seeing as I went to a comprehensive school.”

It seems a reasonable question, so what`s the answer? “Not everyone who goes to comprehensive school has a cockney accent. I think I probably did have more of an estuary accent. Coming from Teddington, it`s more estuary. Cockney is more east London.”

Do an estuary accent then. “No.”

American then. “No.”

Can she do an Indian accent? “Not today, no. Get lost.”

But she`s an actor. “You`re an actor, so act [Oi, she`s stealing my lines]. Give me a script then.”

The new film is called The Duchess, and Knightley is excellent in the lead. It`s about a late 18th century “It girl” called Georgiana Spencer, Princess Di`s great-great-great-great aunt. There are obvious parallels between their two lives, though Knightley wasn`t immediately stuck by them, mainly because, as she says, she was only 11 when Diana died (she`s 23 now).

Georgiana marries a cold fish played, also excellently, by Ralph Fiennes, who is really, really horrid to her. It gets more complicated when Georgiana`s best friend, Bess, moves in, and they live as a joyless menage a trois. Georgiana finds some solace in an affair with young politician Charles Grey, but has to stop seeing him in order not to lose contact with her children. It`s a story of female repression, but also of female strength and survival. It`s also a story about public adoration versus private misery (see what I mean about those parallels?).

Even though Knightley is too young for Diana to have made much of an impact on her life, the difference between a person`s public facade and what`s going on inside is something that seems to preoccupy her. “The way you can have extremely strong people who actually in private are completely breaking down. Everyone does it - presents a front that is actually... No one can ever know what`s going on emotionally inside.”

Is there anything of this, of Georgiana, in her? “Am I very lonely, and terribly trapped, and all the rest of it? No, I don`t particularly look for characters that are like some kind of biography of myself, no.”

It`s a role she didn`t find easy. “I wasn`t particularly confident about it, which I think actually helped - because I don`t think that confidence is always a very helpful thing. I really found it very difficult to get a grasp of her.”

Is she often unconfident about her parts? “There`s always an element of fear that you`re not going to be able to make people believe in the fiction, that suddenly you`re going to be standing there in your dress and wig, and feel like a complete loser. Which is not particularly helpful.”

It is not surprising that she mentions wigs and dresses, because a role for Knightley generally involves her putting on one, or both, of those. This has happened by accident rather than by design, she says. “I think I`ve simply read better characters in period pieces than I have in contemporary, which is a pity. I don`t know why that is. But I haven`t been kind of going, `I really want to do another period film.` I`ve just been led by what scripts I`ve thought were good, and what film-makers I thought were good.”

Knightley knew she wanted to act pretty much from the moment she knew anything at all. Famously, she wanted an agent at three, got one at six, and was making TV appearances by the age of 10. Her big breakthrough was the low-budget British film Bend It Like Beckham in 2002, after which she found herself alongside Orlando Bloom and Johnny Depp in camp, big-budget action blockbuster Pirates Of The Caribbean The Curse Of The Black Pearl. Suddenly, the skinny little girl from Teddington was a major, if unlikely, Hollywood star.

While it may be the Pirates franchise that has brought in those millions (however many there are), Knightley is more serious about acting than to be happy simply being a damsel in distress. She`s done the odd thriller and action film, which have slipped by comparatively unnoticed, but it`s with country houses and the past that she is most associated - Pride & Prejudice, Atonement, now The Duchess. It`s what Britain exports well, she says, and it isn`t hard to find modern relevance under a bonnet. “I don`t think we`ve really changed that much in our essence.”

I`m wondering if that`s it, and whether we`ve seen the full range yet. “Of?”

You. “As an actress? I hope not. It would be quite sad if I said yes. I`ve only been making films for the past five years. You change as a person all the time. And so therefore the way you perceive the world and situations, and the way you portray characters, is going to change. I think that`s the aim.”—Dawn/Guardian News Service