Natalie Portman - more than a woman

Society's attitude to powerful women has scarcely changed in the 472 years since Anne Boleyn was beheaded at the Tower of London, concludes the actress Natalie Portman, who portrays Henry VIII's unfortunate second wife in The Other Boleyn Girl.

"You do see how people were calling her [Anne] a witch for having power, and people do that still," argues Portman. "I mean, we still demonise women in power and we still make them targets of ridicule. It's so easy to call them names and criticise them for having power, for making changes, for being strong. Like Hillary Clinton, who I think is so very smart. It's interesting to me that that taboo is still in place," she says.

In recent years, the focus of public criticism has switched to female celebrities. The strongest vitriol is reserved for those women in prominent positions who choose to use their clout as a political platform or to bring attention to injustice. Jane Fonda, for example, was dubbed Hanoi Jane for her anti-Vietnam stance, while the country trio The Dixie Chicks were reviled for their opposition to the Iraq war.

"It's weird how people get so critical when you have a cause or are passionate about something other than fashion. You become just another celebrity with a cause, which, for some reason, is unacceptable," says Portman, herself having experienced collective glazed eyes whenever she raises the topic of her work with the international aid organisation Finca, which provides loans to small businesses in developing countries, or her eponymous range of vegan footwear.

Likewise she puzzles over media gossip suggesting that she and her co-star Scarlett Johansson, who portrays Mary Boleyn, were at each other's throats during the six-month shoot in the UK. "I simply don't understand where this stuff comes from. I've never been in a situation where I'd step on someone to get what I want. I'm ambitious but not in a negative way," says Portman, perhaps a little naïvely given her 26 years and her Harvard degree in pyschology, and also the fact that the two A-list actresses are cast as sisters fighting for the heart of England's monarch.

"The truth is that it's rare to see two great roles for actresses where they're fighting it out; and it's not really over a guy. Like it seems to be over a guy who happens to be the king but it's really about a power struggle between sisters, between women and within themselves too, and how they perceive themselves. And I was just so excited to get to work with Scarlett," she says earnestly.

"I've been a huge fan of hers since we were kids and it's so rare to get the opportunity to work with someone your age, and particularly another woman your age. I think both of us were thrilled at the prospect of working with a peer. She's a wonderful actress and maybe my best scene partner ever. She was just really in it with me and I felt that we really had a connection and between scenes we would keep it just locked, and have this rapport that gave you focus."

Based on Philippa Gregory's best-selling novel, The Other Boleyn Girl is a tale of sibling rivalry. Mary, the first Boleyn sister to win King Henry's affections, becomes his mistress, only to be edged aside by her conniving sister Anne, who systematically replaced both Mary and Henry's first wife, Katherine of Aragon.

"What I like about this film is that audiences initially assume The Other Boleyn Girl refers to Mary because everyone knows about Anne Boleyn and so they go: 'Oh, but there was this other Boleyn girl who was also the king's mistress before her sister became queen.' But each of them has their own turn at being 'the other' Boleyn girl. And I think in a family with siblings – I mean, I'm an only child so I can only imagine – you take turns at being the prominent one, especially with two young women where, at different times, one of them seems to be the more powerful one."

Watch the trailer for 'The Other Boleyn Girl'

Portman was also excited at the chance to portray such a complicated character: "I'm so frustrated by the number of roles for strippers or prostitutes, or the opposite, like: 'She's the moral centre of the film. She's the pure one. She's the one who makes the man realise who he should be.'

"It's the virgin-whore thing in evidence, to the greatest extent, that most bothers me," says the actress, who, ironically, earned a Golden Globe plus an Oscar nod for playing that very role, as a lap-dancer in Patrick Marber's Closer.

"I also love comedy but anytime I read one it's like the girl is in fashion, she's really into clothes or she just wants to get married. Those are not values that I care to jump the bandwagon on. I'd love to do a comedy but you don't find any where the woman has, like, a real job. Joining the 'All I care about is fashion and boys' club is not who I am, and it's incredibly frustrating."

The daughter of an Israeli fertility specialist, Avner Hershlag, and the Ohio-born artist Shelley Stevens, Portman grew up in suburban Syosset, New York, and was discovered in a pizza parlour aged 11. She credits her solid family background with giving her the ability to move effortlessly between blockbusters such as Star Wars and low-budget independents such as Garden State and My Blueberry Nights, leading to her current position as one of Hollywood's leading ladies.

Making her movie debut as a precocious Lolita-esque girl in Leon, Portman effectively bypassed her teens. In person she is a peculiar dichotomy of woman and girl. While few actresses could manage to squeeze Proust into a discussion of the Tudors, by the same token this brainy Harvard graduate peppers her conversation with a hell of a lot of "likes". Because of this, she comes across as both supremely self-confident and insecure in equal parts.

"I often feel insecure and don't believe in myself. I think we all do unless we're some kind of egomaniacal freak; we all have phases of not feeling so great about ourselves. Either you push yourself to go do something, just to get out of it, and then that whole cycle takes you out of it. Or someone else looks at you and believes in you, and then you get belief from that. There's so many ways to sort of exit that, I guess...

"It would be kind of scary not to doubt yourself. But doubting yourself too much can also become like a sickness," says Portman, who was plagued by anxiety following the release of Star Wars I and II in which she played Queen Padmé Amidala.

"My most difficult time personally was probably my senior college year. I wasn't getting work and everyone hated my performances in Star Wars; everyone thought I was a terrible actress... I took time off and that's when I did Cold Mountain, which I basically had to beg to get even that little, tiny part. And Mike Nichols wrote a letter for me, and having him believe in me and look at me like that, that process slowly took me out of it.

"With almost every performance, I feel like I've failed on some level. But I also think it's very human to feel that when you mess up, you get more out of it than when you succeed. So I think I almost try to get myself to fail on some sort of subconscious way because it really is the thing that changes me most, when you mess up. And if you don't mess up – if you do something that's really hard and really challenging, and where you really could have done the worst thing ever, and then you don't – that's so much more rewarding than if you take something easy.

"But I'm not, like, self-flagellating, I just move on. And it drives you to do better, too, when everyone's saying you're terrible, or you feel like you're terrible. It just makes you want to be good."

Portman might have a psychology degree, but she is realistic about the likelihood of pursuing a career as a therapist: "While I can totally imagine myself in another career, it's a little stranger now that I have more recognition. I mean, if I were to be a doctor it would be a little weird for my patients to think, 'Oh, my doctor is the mother of Princess Leia...' "

Having avoided the tabloid press during her transition between child stardom and adult actress, Portman has discreetly dated actors Zach Braff and Jake Gyllenhaal as well as being spotted recently with former male model Nathan Bogle.

"Dating's hard enough as it is without the whole world knowing about it," she says. "I try to live my life as normally as possibly and that includes my love life. I think so far a lot of what I do in my private life has managed to pass under the radar mainly because I'm so small [she's 5ft 2in]. I don't usually wear much make-up and I dress pretty casually so I often pass unnoticed.

"Everyone has their sorrows or difficult times and nights they're embarrassed about. I've had a few drunken nights. I'm not a puritan. I simply haven't made a lifestyle out of it."

'The Other Boleyn Girl' opens on 7 March