ANOTHER year, another Oscar nomination. Having won the prize for best supporting actress last year for her portrayal of Katharine Hepburn in The Aviator, Cate Blanchett is in the running for two in a row this year, nominated this time for her controversial role as an art teacher who seduces an underage boy in Notes On A Scandal.

But while the fictional character has brought the sought-after actress notoriety, she likes to stay out of the limelight as much as possible. "I'm not running out my front door in my pyjamas into the arms of the paparazzi every morning, " she says.

It's not that she's unfamiliar with the ordeal of being doorstepped. But in her role as an art teacher called Sheba who has sex with a 15-year-old Irish schoolboy - and then moves in with a lesbian colleague who catches her at it to keep her quiet - she experiences much worse.

"I enjoyed playing it because I'm not living it, " she says. "I'd go home afterwards thinking, oh thank Christ I'm in a happy relationship."

Thirty-seven-year-old Blanchett, despite her distinctive wide lush lips and penetrating blue eyes, is never herself in movies, which perhaps explains why she's so much in demand. She has three other movies coming out this year - the Golden Globe award-winning Babel, Steven Soderbergh's The Good German, in which she plays a war-time spy, and Shekhar Kapur's The Golden Age, a sequel to her breakthrough, Elizabeth - having just finished filming Todd Haynes's Dylan. She is currently back with Babel costar Brad Pitt shooting David Fincher's The Curious Case Of Benjamin Button.

"I'm not interested in playing characters who think the way I do, " she says. "I played mothers before I was a parent. It's the old cliché, you don't have to murder somebody to play a mass murderer."

Right now she's being her nononsense Australian self, although she's dressed anything but casually. She has a black puff-sleeved dress, taken in tightly at the waist, with a puffed-out mini-skirt and pink fishnets that show off her long legs in knee-high Armani boots. As she talks she fiddles with a gold wedding ring, turning it around on her finger.

"I found the love scenes with the boy very confronting - one of the most difficult things I've done, " she says. "I had to be aware that I was the adult in the situations, yet my character was perceiving it - or trying to perceive it - as a man and a woman. The actor was above the age of consent, but still he was a young boy."

The role of her under-age lover is played by Andrew Simpson, the Donegal actor who made his debut in Song For A Raggy Boy. Did she feel that there was something about his Irishness that was good for the character - a poetic streak that plays right into the woman's fantasies and her justifications for falling in love with him?

"What are you saying about yourself?" she teases. But surely she noticed when she was filming Veronica Guerin in Ireland how reckless the Irish can be, plunging into things without a thought?

"Well Andrew was very open and enthusiastic, and up for it, " she concedes. "But I can't imagine doing what Sheba does, breaking apart her life in such a spectacularly devastating way. I can't personally understand the attraction of younger men. If I had a 15-yearold son some art teacher was bonking her brains out in the art room with I'd be in there with a meat cleaver.

"I still think she's an adult and he's a student. Perhaps if they'd met at a party the boundaries would have been different, but there's a responsibility that goes along with being a teacher. And Sheba knows the boundaries that she's transgressing. I don't think that film at all seeks to justify her actions or explain them in any simple way. Nor is it the centre of the film.

"The centre of the film is the relationship between the two women. The act with the boy is just the catalyst that propels her into her predatory colleague Barbara's arms. I think it's important that the transgression is enormous from a dramatic point of view because Barbara needs to be the keeper of an enormous secret.

There are few taboos left in society, but this is one of them."

The film has won widespread acclaim for its handling of these difficult themes. Judi Dench, who portrays Barbara with devastating conviction, has been nominated for a best actress award. Dench provides the unreliable narrator voiceover that lures us into her warped world, and the fact that she had worked for Richard Eyre before, playing Iris Murdoch in during filming.

"Obviously they had this shorthand with each other. It made for a very buoyant and open set, more like a rehearsal room really. It meant you could just chuck your lot into the ring and see what happens. Judi was incredibly easy to work with.

"We met around Richard's kitchen table for a couple of weeks sussing things out. But until you get up there together before the camera it doesn't amount to anything."

Ultimately, Notes On A Scandal - adapted by playwright Patrick Marber from Zoe Heller's novel with a dark humour that gives an edge to even its more melodramatic moments - is a portrait of two incredibly isolated and lonely women who go to extraordinary lengths to form connections with people, Sheba with a 15-year-old pupil and Barbara to cleave Sheba to her breast.

"What the film does explore is the nature of so many unhealthy bonds that we all make, " says Blanchett. "Not all our friendships are healthy or equal ones. Patrick explores the unpalatable side of the human psyche, the unhealthy side of our connections with people, the need we all have that we don't admit to anyone, let alone to ourselves."

To get into their roles as the fatally enamoured teachers, Blanchett and Dench stood in at classes at an inner London comprehensive school. "We found it the most terrifying encounter we'd ever been through. It sent shivers down Judi's spine when she had to stand up in front of a class. She was barely able to look up, because adolescent boys and girls are terrifying.

"Also, the techniques of control teachers used to rely on when we were at school are now considered reprehensible."

So was Blanchett a good girl at school. "No, " she says, demurely.

The daughter of an American naval officer, who settled in Australia to be with her mother - a teacher - she was educated in an exclusive girl's school in Melbourne of which she now says, perhaps wisely, "I've rather forgotten my childhood." Geoffrey Rush spotted her in a student production of Electra and cast her in David Mamet's Oleanna in 1993.

Then both Bruce Beresford, who was filming Paradise Road, and Gillian Armstrong, who wanted her for Oscar and Lucinda, fought over her. "I was lucky from the start because I didn't have to go through that hanging around, waiting for Hollywood, " she says.

"I've never been very front-footed about those things. I find it hard to say, cast me, cast me. I'm very withdrawn about that stuff."

When we first met on the set of Veronica Guerin, she told me that she was drawn towards playing women who made a difference, whether as the Virgin Queen in Elizabeth, the war-time spy in Charlotte Grey, a mother who goes after the Apaches who abduct her daughters in Missing or Katharine Hepburn in The Aviator, not to mention Galadriel, Queen of the Elves in The Lord of the Rings.

Yet more recently her roles have tended to be more women to whom things happen rather than those who make things happen. "I always look for fragility - the fault-lines in a character - and try not to define them as being strong or not strong, " she says. "We all have our weaknesses."

On winning a best supporting actress Oscar for The Aviator, she says, "I thought it's a bit of a curse.

The phone is going to start ringing now because there's a sense that suddenly you've arrived somewhere." Then she shrugs, "Not that you feel you have yourself, but you're perceived to have, and they're always looking for the next thing. But fortunately the phone hasn't stopped ringing."

She first came to England as an 18-year-old backpacker. Since marrying her Australian screenwriter husband Andrew Upton in 1997 - just before she won a Golden Globe for Elizabeth - she's lived in a three-storey Georgian house in North Islington, London, but the couple have now moved back to Australia to work together as co-artistic directors of the Sydney Theatre Company until 2008, a decision influenced by the fact that their eldest, five year old son Dashiell has now started school.

"It means needing to be in one place from now on, " she says.

Their opening production last November was a double bill of Harold Pinter's A Kind Of Alaska, which she directed, and a David Mamet play directed by Upton.

"Putting these two great writers together in close dialogue in the one evening became an electrifying proposition, " she says. "I feel there are lots of latent skills I've been developing that hopefully will benefit the company. The fact that my husband is a writer and I'm an actor and that our strengths and interest is the text and performance opens up all sorts of opportunities. We hope that eventually the company will tour."

Her return to theatre has prompted speculation that she's taking a break from movies.

"That's just the black or white nature of the media, " she says. "I'll be more than happy to do a film every year or every other year. It's all about timing and what the role is and how my kids are. It's contingent on a lot of things, as is life."

She had no qualms about saying yes to the Bob Dylan movie. "Todd Haynes has divided Dylan's persona into five or six different characters, none of them called Bob and each of them played by different actors and shot in different ways. Mine was in black and white and, as he said, 'after Fellini'. It's very strange and fantastic, and by no means a biopic. The fantastic thing about Dylan is that he's constantly escaping definition and reinventing himself."

Not unlike Blanchett in her choice of roles, perhaps. "I love the challenge of the unexpected, " she says. "I don't understand a way to work other than boldfacedly running towards the future. It's always good to take on things that at first seem bigger that you."

'Notes On A Scandal' opens on 2 February, 'The Good German' on 2 March. 'Babel' is on general release