I'd read enough about Ewan McGregor to anticipate that interviewing him could well involve an arduous amount of carousing and falling off bar stools. He is, after all the actor who turned a photoshoot with Elle magazine into a marathon bender at a Covent Garden pub, who got plastered on whisky at a Versace show in Milan, and who collapsed in a mock-faint after being introduced to Naomi Campbell. Boozy high jinks have been the leitmotif of McGregor's public image- he seems to have spent half his career amiably slagging off Eddie Murphy, Sean Connery and other luminaries- while sharing a lager or six with journalists. Gossip from Sydney, McGregor's adopted home for the past eight months, suggested business as usual: he'd been spotted partying on Tom Cruise's yacht on New Year's Eve, at a Chemical Brothers' knees-up and drinking Guinness on the set of Baz Luhrmann's new film, Mouin Rouge.

But when I finally meet McGregor at a brasserie near the city's King's Cross sleaze strip, I find him quietly sharing a bottle of mineral water with his elfin wife, the French born set designer Eve Mavrakis. It doesn't take long to surmise that today at least, Scotland's favourite loudmouth is cutting a different profile. Sartorially, McGregor is as offhand as ever: white singlet, baggy shorts, sandals, a finger-combed thatch of hair, no shades. But even after his wife leaves, he sticks to the water, and for much of our two-hour lunch he does a good impression of a man choosing his words carefully, avoiding controversy. But it would be misleading to suggest that McGregor's antic spirit has suddenly seen stifled by the weight of celebrityhood. When he lets loose one of his mouth-gaping laughs, his eyes still have the same wicked gleam which lit up the final frame of Shallow Grave. Mischief-making is never too far from the surface, as he proved recently while filming Eye of the Beholder, a psychological thriller in which he plays a surveillance operative tracking a serial killer (Ashley Judd) across the States. The story goes that in his off-duty hours, McGregor began stalking Judd in order to flesh out his performance. "I didn't stalk her," he counters, then allows a faint smile to crease his face. 'But I did use to practice a wee bit… I got some photographs stuck in her door, saying "I'm watching you" with different parts of my body showing behind curtains and chairs. But just as a joke- I wasn't actually following her.' However this backfired when Judd, who had herself been harassed by an obsessed fan, thought the photographs were from a stalker. 'It didn't go down to well,' he admits, putting his hand over his mouth like an errant schoolboy.

Although McGregor tries to detach himself from the usual conventions of stardom, he is still wary of fame's pressures. He mentions one lesson particular, which happened during the promotional blitz for The Phantom Menace. Six months before its release, he gave a typically frank interview in which he said working on the film had been 'tedious' and playing Obi-Wan Kenobi had not exactly pesented a major psychological challenge. After concerned calls from Fox executives, McGregor spent much of the ensuing months 'clarifying' his remarks. "The press around Star Wars was just insane," he says. "I was in Hello! Magazine and I've never done an interview with Hello! in my life, nor would I ever. It really offended me."

McGregor didn't realise that an interview he had given during a press junket would end up in Hello! "I was on the front page looking like a big dick, claiming Why Fame Is Less Important To Me Than My Family. I was mortified." Barely are these words out of his mouth than McGregor is suddenly back-pedalling mimicking his own outrage. (Hello! Insists that its interview with McGregor was properly bought from a reputable press agency.) Stephan Elliott, the Australian director who worked with McGregor on Eye of the Beholder saw the effect of the Star Wars juggernaut at first hand. "The media attention around him quadrupled, to the point where Ewan became aware that anything he said might be pulled ou of proportion. It got a little ugly for him."

The result, as McGregor himself admits, is that he simply isn't as freewheeling as he used to be. "I'm afraid I've become less like that," he says, taking a drag of his cigarette. "Maybe it's just growing up." As an up and coming actor, he bucked the angst-ridden star in therapy schtick by confessing the awful truth: he was an ordinary middle-class boy from Perthshire, who never really doubted that he would make it. As a movie star he has tried to retain that same ethic. McGregor has never had a publicist and is blithe enough to allow his mum, Carol, to act as his official spokesman. At one point I try to prod him by mentioning a recent crack by Scottish actor Dougray Scott ('I'm not in this business to be a heart-throb. Thank God I'm not Ewan McGregor'). "I think Dougray's just having a wee dig through the press," he says affably. "I'll think of a cracker to say about him in a minute." Still, the giddy rocket-ride that shot McGregor from Trainspotting to Star Wars in a few years has recently entered a more turbulent phase. At 29, he's negotiating the tricky transition from Britpack wonderboy to serious actor. Critics forgave his wooden performance in Phantom Menace; but they've been less kind about Eye of the Beholder, which received scathing reviews when it was released this January in America. So there's a lot riding on his latest film, Nora, in which McGregor not only plays one of the most celebrated literary figures of the modern era, James Joyce, but also shares a co-producer's credit.

Four years in the making, this stately 9 million historical drama is the first full production from Natural Nylon, the company McGregor formed with fellow actors Jude Law, Johnny Lee Miller, Sadie Frost, and Sean Pertwee. McGregor was instrumental in getting Nora made-he signed for the role in 1996, shot test scenes to help the producers raise money, then rescued the project by taking it to Natural Nylon and meeting distributors after the original backers pulled out. 'I'm proud that we made it with European money, and that we didn't have to answer to anyone from America.' The film centres on the early years of Joyce's relationship with his wife, Nora, and director Pat Murphy doesn't avert her gaze from the darker side of Joyce's psyche, which he left for posterity in the infamous 'dirty' letters to Nora, which recorded his sexual fantasies. 'God they were quite up for it weren't they?' laughs McGregor. 'Some of those scenes are actually quite disturbing -they're not giggly pillow-fight sex scenes. We shot all of those scenes back to back, so that was a heavy 10 days. I never take my work home with me, but when you've been doing days like that it's something you've got to get out of before you get home.' McGregor whose non-method acting style is legendary (his preparation for the Phantom Menace fight scenes included downing a couple of beers) didn't radically change his technique. He arrived at Nora auditions so under-researched that when Murphy asked what he knew about Joyce, he said, 'I don't know anything about him at all.' This is part and parcel of McGregor's onscreen appeal- the sense that you're watching someone fly by the seat of his pants. The roles that got him noticed- the cocky journalist in Shallow Grave; the loquacious junkie in Trainspotting; and the translator in The Pillow Book- had a daring that went beyond the well-chronicled flashing of the McGregor member in Velvet Goldmine. Those films of course, were all made in the early Nineties when McGregor was living life at full tilt; the communal crash pad in Primrose Hill, the wild partying. Since then, his career has been a brave attempt at combining indie filmmaking with a parallel career as the richly rewarded star (a rumoured 5 million per film) of Hollywood's most successful sci-fi series.

McGregor still waxes nostalgic about the making of Trainspotting six years ago and recalls being in Glasgow with co-star Jonny Lee Miller and author Irvine Welsh being mobbed by fans yelling, 'Rent Boy! Sick Boy! Irvine Welsh!' For him Scotland figures as a place he can re-discover some semblance of normality. 'I love being up there. When I was at drama school I used to go back all the time on an overnight bus from Victoria to Edinburgh. The sun starts coming up at 4am just as you reach the border and it's all green…' There was a time around the Trainspotting phenomenon when everything clicked into place for McGregor: he married Mavrakis, 37, whom he met on the set of Kavanagh QC; their daughter Clara was born in February 1996, the same month Trainspotting was released; and McGregor was anointed Britain's hottest movie star- all before his 25th birthday. 'God,' he told The Face, 'I'm so f**ing lucky.'

Then he took on 10 films in four years and the picture became muddier. McGregor's choices didn't always seem wise in retrospect- does anyone recall Nightwatch or The Serpent's Kiss?- and even his strong performances failed to salvage films such as Rogue Trader or Velvet Goldmine. Elliott notes that the scattershot nature of McGregor's work has 'made him hard to peg. He's had some good successes and some major flops.' McGregor defends his choice of films: Phantom Menace was 'an interesting thing to have done'; Eye of the Beholder, 'a spectacular piece of filmmaking'. Still, he acknowledges that by the end of 1998 he had worked himself into a hole. 'I got very depressed. It was just too much. I had agreed to do films such as Rogue Trader and Little Voice, and they all jammed up against each other. In one case I had less than 12 hours off between one film and the next.' Does he think his work suffered? 'No, I don't think so. Maybe.' I tell him there's a preception that he's been the best thing in some not particularly great films. 'I know there was that criticism but what does working too much mean? It's nobody's business but mine. They were all stories I wanted to tell.' The recent strained relations between McGregor and director Danny Boyle are symptomatic of McGregor's struggle to resist the distorting effects of money and Hollywood values.

There was a giddy period after they made Shallow Grave, Trainspotting, and A Life Less Ordinary, when the pair were shaping up our very own Scorsese/De Niro partnership. But they have barely spoken since last year when the actor castigated Boyle for casting Leonardo DiCaprio in The Beach rather than him, and accused Boyle of chasing Hollywood mega-budgets rather than sticking to his principles. Today McGregor says he is keen to work with Boyle again,m but doesn't offer much evidence to suggest this is a likelihood. How is their relationship? 'It's fine.' A quick exhalation of smoke. 'It's fine.' End of subject. Last year, McGregor took a widely praised turn on stage at the Hampstead Theatre in Little Malcolm and his struggle against the Eunuchs, directed by his uncle, Denis Lawson. It was part of a move to wind down the globetrotting workaholism of the previous two years. After Nora, he moved to Sydney to work with Nicole Kidman on Moulin Rouge, the much anticipated period musical by Baz Luhrmann. It's a project that suits McGregor's modus operandi, a big-studio film by a director who works at considerable creative and physical distance from Hollywood. Moulin Rouge has been shrouded in secrecy. 'I'm not allowed to say anything other than it's going fine.' He has turned the Sydney sojourn into an extended respite from the constant attention of Londoners. As usual, his family came along for the ride; renting a house in the suburbs and enrolling Clara into a local kindergarten.

Like most aspects of McGregor's career, there's a seeming contradiction between his reputation as a hellraiser and his avowed desire to maintain a normal family life. And like most celluloid sex objects, he endures constant speculation about his private life- when he and Rogue Trader co-star Anna Friel were photographed kissing off-set, his publicist released a 'just good friends' statement. McGregor may have ranked second only to George Clooney in an internet poll of female fantasy figures, but he plays down that aspect. 'I never percieve myself as that kind of thing. I only worry about my work- I don't walk around thinking of myself as a heart-throb.' What about the pressures on his marriage from all the adulation? 'I'm not usually aware of it. We travel together my family and I it's not like we spend months apart, so it's fine.' Naturally, I find this hard to believe. But then, McGregor swears he hasn't been propositioned by a single female during his Australian stay. Susan Lynch, his co-star in Nora, corroborates what most of McGregor's friends and colleagues say- that privately he's down to earth. 'I don't think the fame thing has affected him at all, and I don't think it will.'

This month McGregor and family move back to the large north London home which they bought 18 months ago but have barely seen. In two months time he'll return to Australia to film the second of his three Star Wars films. But it's evident that McGregor sees Hollywood primarily as a means to an end; he wants to produce more films, do more stage work, and have another stab at directing, after the 10 minute short he recently made as part of the Tube Tales collection. It's a seductive dream- that you can have fame, adulation and get paid millions of dollars while somehow hanging on to the spirit that first fuelled you.

Perhaps McGregor can defy the odds. Just after our interview, he turns up at Sydney's Gay and Lesbian Mardi Gras, sitting amid the punters with his wife. He's wearing a leather suit, mascara and red lipstick and as the parade passed he suddenly vaults the barricaes and starts gyrating, clutching some liquid refreshment, striking poses. The spectators recognize him, begin chanting, 'Go Scotsman, go!' and McGregor basks in the cheers for a few minutes, flashing that joker grin.

Then he returns to his wife and becomes just one of the crowd.

Almost.

Nora is released on May 19