Season of the Witch

Tilda Swinton as the White Witch.

Tilda Swinton strides into the room for questioning like a pro wrestler enters a ring - with an aura that says, "Throw 'em at me". Even casually dressed and free of makeup, she is striking, with small, opaque eyes and translucent skin.

Today is her 45th birthday, yet Swinton has an almost ageless appeal, no doubt part of the reason she was cast as Jadis the White Witch of Narnia in Andrew Adamson's The Lion, the Witch and the Wardrobe. With a costume fit for an ice queen and some clever special effects, it didn't take much to turn this Scottish actress into a despot of the perpetually wintry otherworld.

Ask Swinton why she got the part and she replies simply, "Tall, white, evil".

But as the world waits excitedly for the multimillion-dollar adaptation of C.S. Lewis' famous children's books, it's hard not to wonder how Swinton came to be here.

The Beach aside, most of her roles have been daring choices in smaller, artistic films: a transsexual in Orlando, a grubby bartender in the Francis Bacon portrait, Love is the Devil, and more recently, a psychiatric nurse in the popular festival film, Thumbsucker.

Swinton was to the late maverick film-maker Derek Jarman what Uma Thurman is to Quentin Tarantino. Next year she plays Velvet Underground's Nico in the film of the same name.

The daughter of Major-General Sir John Swinton, OBE, Swinton was born into the establishment, went to school with Diana Spencer and articulates her vowels with such precision one despises one's New Zillund accent.

So what made this child of the aristocracy, queen of arthouse cinema, agree to star in a mega-budget Disney film?

Her children, as it turns out. Despite never having read any of the seven chronicles, Swinton initially thought the job offer a crazy idea. "Well, it's a tall order to play the epitome of all evil."

It wasn't until she read the book to her 7-year-old twins, Honor and Xavier, who rather liked it, that she took the offer seriously.

She was also attracted to the idea of working with Kiwi animation king, director Andrew Adamson, the man behind the Shrek films, because she felt privileged to be one of the first humans he has "operated".

When she arrived in New Zealand she took a road trip to Napier to get a feel for the place. "And it just continued to look like Scotland so I came back."

During the shoot she thrilled in the special effects, the inventiveness and experimental nature of film-making, even on this large scale.

She doesn't appear much in the film, comparing herself to Jaws, but her character's design was larger than life, requiring an ever-changing costume and an immense ice castle. The film was shot north of Auckland, and two huge warehouses were devoted to her reign of terror, one of them strewn with creatures Jadis has frozen in time.

"I've worked on a couple of other big films but never been in this position. I always kind of breezed in like a mascot."

She suggests it might have made the publicity for the film much easier if she had in fact been "a right bitch" and says she was a disappointment by being friendly to people when the cameras stopped rolling.

Ask her how she got into character and she shakes her head. There is no such process for Swinton - she doesn't know how to talk like an actor, let alone talk herself into a role. She simply hops into the costume, and becomes her.

"I have this fantasy that she doesn't really have a body, she's this alien and she goes, 'I need a dress!' and covers herself in a bit of Narnia.

"The dress is like the bottom of an amazing waterfall I saw at the Huka Falls. It's like she's made of water, or ice or smoke or something natural.

"Being the epitome of all evil, she is covered in fur. She has hair that doesn't look like hair, it looks like it's come from the ground, like roots, and her crown is made of ice. It's not going to look like a costume that she got out of a wardrobe. And I wish that I was wearing a green suit and we CGI-ed it. It's really difficult to wear."

If Swinton is intimidating enough without her witchy alter ego, she's about to become the stuff of nightmares. Jarman once told her about a woman on the subway in New York who petrified him - it wasn't until he was safely on the platform that he realised she had been the Wicked Witch of the West in The Wizard of Oz.

"I'm going to have children backing away from me for the rest of my life. I'm sort of prepared for that."

The first scene was the most difficult, because it's the only time we see Jadis with her guard down.

"I told Andrew that my aim was to make sure that if you stopped the film at that point and you asked the children in the audience they would have said, 'Edmund has just met a really gorgeous and really nice lady in a sleigh', with absolutely no idea. The adults might have an inkling of something sinister but the children wouldn't, really. In that sense she is like the most practised paedophile."

She shrugs, concedingly, that the film could be the next big fantasy franchise like Harry Potter or Lord of the Rings - "What will they do next? Milly Molly Mandy, the series?" - but isn't worried it could potentially spawn six more films, perhaps because the White Witch appears in only two of the books.

The books' hotly debated Christian themes don't bother her, nor the fact her character is so Aryan in a World War II context. "For my money, this is the story of a war child's consciousness and we start this story of this film very much in a war-time environment.

"I think it's a super-cool, incredibly important story, especially for children. All of our children are war children now."

An animated version of the film incensed her, particularly when the actors said, in their American accents, that they had gone to "stay" with the professor.

"You don't stay with the professor," she snipes, "you were billeted because you were English for a start and you were being bombed out by the Nazis."

She is just as riled by American politics, and speaks of her experience on last year's jury at Cannes, where her vote helped Michael Moore's documentary Fahrenheit 9/11 to win the top award, as though it were a United Nations conference. But there are more pressing dilemmas to discuss, like how would she feel if she was made into an action figurine?

"Yes, that's going to be a challenge," she says. "The thing I'm most concerned about is the idea of Disney not being able to resist tying in with McDonald's. I'm already wondering about that. What are they going to put on that burger to make it white?"

LOWDOWN

WHO: Tilda Swinton, the White Witch in The Lion, the Witch & the Wardrobe.
BORN: November 5, 1960
KEY ROLES: Orlando (1992), Blue (1993), Love is the Devil (1998), The Beach (2000), Young Adam (2003), Thumbsucker (2005), Constantine (2005).
TRIVIA: Is a former member of the Communist Party of Great Britain.