Swinton's ability to weave between commercial blockbusters and the edgy fare of art-house films makes her one of the most remarkable actors of her generation. Narnia might have provided her with ample financial rewards and career opportunities in Tinseltown - which, not surprisingly, she has yet to cash in on - but the 46-year-old remains loyal to her roots in the more intimate and engaging productions in which she made her name in the 1980s under the aegis of Jarman, a mentor of sorts for the actress since she left a potential career in classical theatre to become a mainstay in his screen explorations of sexual politics throughout history.

But Jarman is no longer the be-all and end-all for Swinton. When she takes her seat in a heaving pavilion at Cannes, it's to talk about Tarr's The Man From London, which was competing for the Palme d'Or at the city's annual film festival. She plays Mrs Maloin, the wife of the film's railwayman protagonist, a sombre man whose mundane existence is thrown into doubt when he retrieves a suitcase filled with British banknotes.

True to style, Tarr's latest film is driven by long, meticulously choreographed takes (29 in a 132-minute film), with minimal action and dialogue. Swinton appears in two scenes, one of which begins with her seated at dinner with Maloin (Czech actor Miroslav Krobot) and their daughter (Erika Bok) - and ending, after minutes of fluid camera movement through their flat, with a screaming match between the couple. 'The work is incredibly technical, which I love,' says Swinton. 'Because I'm a film nerd around the technical aspects of film. I like the fact that they attempted to make something magical and elusive as something really practical: the track will be here and the light is like this. I like that. And with [Tarr] it's a joy because it's all technical - for 16 hours, it's a question of how the camera can move around the back of your head and then come around here. We have to move the table out of the way and put it over there, and you have to get out of the way and then you have to come around, and you have to go over there and get on a boat.'

Tarr's films are known for portraying their characters as disconsolate zombies losing all passion for life. The bust-up between the Maloins in The Man From London provided a moment of explicit physical frisson that's otherwise nearly absent throughout the film. Although it's again a showcase of Swinton's dramatic skills, the scene is unique in the way she and Krobot deliver their lines in their native languages (later dubbed into Hungarian).

'I was shouting in English, Miroslav was shouting in Czech, and everybody else was shouting in Hungarian - and nobody understood a word anybody else was saying. It was very harmonious.' Swinton says she has also re-recorded her lines in French ('with a Polish accent') for the film's release in France. 'The film isn't about understanding - it wasn't really necessary for us to under- stand each other. I remember Bela showing me a test years ago when we were preparing for this film - two years ago when I was in Budapest. There were two people talking to each other and shouting in one of these scenes. You can see that someone's not listening in the way that you don't listen when you're having a fight with some-body. You just aren't really interested in hearing them - you just want to do your own shouting.'

Swinton mightn't be partaking in any more sparring matches in future projects, but the variety in her films remains a constant. Although she attended Cannes as a torch-bearer for one of the most left-field films in competition this year, she'll be at the Venice Film Festival two weeks from now promoting Michael Clayton, a Hollywood thriller starring George Clooney, Tom Wilkinson and Sydney Pollack. In the film - which is in the competition for the festival's top-prize, the Golden Lion - Swinton plays a high-flying litigator, Karen Crowder, whose upward trajectory at work is on the brink of collapse when a colleague, weighed down with guilt for siding with a transgressing company, threatens to sabotage a multimillion settlement for a class action that Karen is overseeing.

This will be followed by a foray into the Mexican desert in Erick Zonka's Julia, the French film- maker's first American film, about a recuperating alcoholic's escapades with a young boy she abducted. Then it's back to blockbuster territory with David Fincher's The Curious Case of Benjamin Button, with Swinton starring opposite Brad Pitt in a fantasy romance about a man experiencing time backwards. And then swiftly she returns to the idiosyncratic: a role in Marilyn Manson's directorial debut, Phantasmagoria: The Visions of Lewis Carroll.

Swinton's family background is an interesting contrast with the transgressive work she does on screen. The daughter of John Swinton, a major-general and former chief of the Household Division at Buckingham Palace, Katherine Matilda Swinton spent her early years in some of the most aristocratic educational institutions Britain has to offer: West Heath Girls' School (also the alma mater of Diana, Princess of Wales), Fettes College and then Cambridge University. Her departure from political science to drama after graduation was a surprise - an act that she matched two years later when she left the Royal Shakespeare Company.

Such spirits will be revived next year with a pair of projects that will unite Swinton with other Jarman alumni: she plays Lady Macbeth in an adaptation of the Shakespearean play by John Maybury (who most recently directed thriller The Jacket, but who made his name as editor of The Last of England, and a behind-the-scenes mover in many other Jarman films) and starring Sean Bean, who found fame in a debut role in Caravaggio, as Macbeth. Then there's a documentary on Jarman's work, to be directed by Isaac Julien.

Although Swinton has gone on to greater things, she looks back on the death of Jarman in 1995 with much anguish. 'There are two reasons why it's difficult,' she says. 'One was personal, because I lost my best friend. The other reason was related to Derek's success - there was a huge shift at that time and the sensibility in which we [art film directors and actors] were safely working in Britain at that time. The trapdoor just went shut. It's impossible. There was no funding any more. The [British Film Institute] production board stopped funding films and eventually was dismantled, and cultural films became almost impossible to fund in Britain.'

Then, members of Jarman's circle dispersed. 'We were so tired and so many of our friends had died [of Aids] and everybody went quiet for a while - for 10 years,' Swinton says. 'Some people went away to work in different ways, some people had twins [Swinton is the mother of two nine-year-olds, with artist John Byrne]. We all started to regroup a few years ago.'

As she moves more towards the mainstream, Swinton says she's confident art-house film is on the rise again, and that directors such as Tarr and Jarman will eventually be embraced by a young generation with access to past gems on DVD.

The Man From London, Aug 18, 4.15pm, Hong Kong Arts Centre; Aug 19, 7.45pm, Hong Kong Science Museum (part of Summer IFF). Michael Clayton opens on Oct 11