In his lime green and white one-piece leathers, Renton number-one cut and Sidi Vertebra biker boots, Ewan McGregor bears a passing resemblance to Buzz Lightyear's less bulky brother. He's been chatting amiably with the Brands Hatch officials, instructors and club members who have gathered to request his autograph and to talk torque and handling. Now that it's time to join them on the track, he takes a moment to focus. He falls uncharacteristically quiet and still. This is disturbing. I don't doubt his prowess round Brands Hatch race circuit, but he planted a seed of worry earlier when he pointed across the track to the steep left-hander where he crashed the last time he raced here. Totalled his bike.

Thoughts like insurance and are we covered? And it's Obi-Wan Kenobi and oh ***** richochet round my head as we wave Ewan and his pal, fellow actor Charlie Boorman, off on their first circuit. Esquire is taking a national treasure-one of our most talented young actors, a man whose name can green-light projects, a Hollywood A-list name-and letting him loose on his box-fresh Honda Fireblade CBR900RR to rev and scream round the circuit at 100mph in the blinding sunlight and oily heat of a perfect summer's day. Sitting in the late afternoon sun on a balcony in the more sedate and elegant surroundings of London club Home House, Ewan McGregor and I study a newspaper story detailing Hollywood's fad du jour. Illustrated by a colour photo of a pert and shapely female posterior, it reveals that buttocks are the new breasts and implants are now available to achieve J-Lo sphercity.

Three minutes into our conversation, Ewan reaches across to the discarded paper and turns it over to make the image disappear. He apologizes with a smirk. "Sorry, I can't stop looking at her beautiful big black bum." It's not good for him to be distracted. It takes away from his energy, which fires his passion. This passion, this enthusiasm, of his is so intense it's contagious. It's so palpable you feel it pulling you along willing in his wake. We're talking about Moulin Rouge, his latest film to hit British screens. It's a great spectacle, a real cinematic treat: an all-singing, all-dancing extravaganza set in turn-of-the-century Paris.

With the whole trinity of Ewan McGregor, Nicole Kidman, and director Baz Luhrmann, none of them a slouch in the manic energy department, it must have been an explosive collaboration. "Baz kept it feeling like a threesome all the way through, all of us driving it. We rehearsed for four months, and he turned our work into the pages of the script. He very cleverly drew us into his world of the Moulin Rouge in his head. So by the time we started filming it was second nature for us to be singing to each other and it didn't feel in any way awkward."

Moulin Rouge is more than a musical; it's an opera, a sumptuous, absinthe-fuelled vision, but with contemporary songs that continually change the game. At its core is a tragic love story. It's based on the myth of Orpheus, and tells the story of Christian, played by McGregor, and idealistic writer seeking bohemian revolution, decending into the underworld looking for perfect love. "Yeahyeahyeah…I knew it would be a big deal and huge in scale. But I didn't for a moment imagine it would have such emotional turmoil in it. Those two scenes when I'm tearing out my heart, ***** me." Nicole Kidman plays the top courtesan in the nightclub/bordello Moulin Rouge.

How was it working with Nicole? I hear you took to calling her a skanky whore. "A high class skanky whore. She was excellent fun. I suppose you're so used to seeing her on magazine covers and being Mrs Cruise and all that stuff. There are a few actors or actresses where when you meet them you're a bit…starstruck, I suppose. But with her you get over that immediately. She's so funny. I'd tell rude jokes and swear and belch and fart and she'd be like a big sister and go, 'Ew-an, Ew-an'. She'd do it when I embarrassed her or if I was spending to long chatting to some of the cancan dancers, and I'd have to go and speak to her. Hahaha."

They would keep each other in check, pulling each other out of lows. "She's a big darling." Firing up another in a regular chain of Marlboros, he has no hesitation at the thought of working with Kidman again. "Yeahyeahyeah. What was great about what we did is that there was a real tenderness and warmth. There's a scene where she's watching me writing and there's something gorgeous and soft about the way she's looking and the relationship you see between us. It would be lovely to do more of that…something contemporary, without singing and dancing, and dangerous and silly. She could do anything, really."

They clearly got quite close. But that's all, despite the inevitable rumours. AS director Baz Luhrmann explains: "You can't spend all day playing lovers and having fun without there being something in the air. We all work in the business of illusions, so we recognise and enjoy that. But we also recognize that it has a border…As far as I know, there was a line. It just didn't happen. But it was very close. I mean, look, they're two gorgeous people."

When the good lord above divvied up his bounteous gifts, he certainly gave Ewan McGregor a double shot. He's a zealot in his search for the craic, a smart romantic with a huge, powerful addiction to seizing the day and sucking it dry. With a helping of confidence the size of Alaska-which somehow stops short of arrogance- and an easy-going charm that gets him out of any tricky situation, he possesses a formidable personal arsenal. He can do edgy and sweet, do snappy banter and honest explanation, take huge risks, admit to vulnerability.

Baz Luhrmann has said about his work in Moulin Rouge, "What you get out of Ewan is a deeply romantic person, but the emotional depth you see in him is truly remarkable." He hasn't exactly been languishing in the emotional shallows up to now. As the McGregor oeuvre shows, he's a versatile actor. Inspired by his mother's brother, actor Denis Lawson, at an early age, he left school at 16 to work at Perth Repertory Theatre in Scotland, then hot-footed it to London's Guildhall drama school. His big break came soon after graduating, with Dennis Potter's acclaimed TV series Lipstick on your Collar. His movie debut followed swiftly. He won critical waves for the raw energy of Shallow Grave, then worked with the same trio of director Danny Boyle, producer Andrew MacDonald and writer John Hodge to make the ground-breaking Trainspotting. He put down the syringe and donned wig and to hat for Emma-pausing only to get married to French production designer Eve Mavrakis- and played opposite Cameron Diaz in A Life Less Ordinary.

He blew the horn in the excellent Brassed Off, and worked with director Mark Herman again on Little Voice. Natural Nylon Entertainment, the production company he formed with old friends Jude Law, Jonny Lee Miller, Sean Pertwee and Sadie Frost, recently made Nora, about James Joyce. Following a deal struck this year with a big West End theatre group, Natural Nylon plans to go into theatrical production. This excites Ewan, whose most recent stage appearance in London was to rave reviews in Little Malcom and His Struggle Against The Eunuchs, revived and directed by his Uncle Denis.

"The best of times, " he says. He'd always eschewed Hollywood: "It would soon bore me to death- driving round in this Valium lifestyle, you'd soon lose critical faculty."

But he embraced the mainstream two years ago as the young Obi-Wan Kenobi in the first Star Wars prequel., The Phantom Menace (Uncle Denis played Wedge Antilles in the first Star Wars). Of course, Ewan had to do it when asked: "It would take a bigger guy than me to turn down Star Wars." And he wanted a light sabre. "I follow my instincts on what I want to do. It doesn't really matter to me what it is, budge-wise or whatever," he says. He's one of the few actors who is in the comfortable postion now of being able to dabble in Hollywood and still hold on to his integrity.

Ewan's just back from four months in Rabat, the capital of Morocco. He was filming Ridley Scott's latest, Black Hawk Down, a true-life story "about a battle that happened on 3 October 1993 when the Americans went into Somalia." He's always wanted to do a war film, he says, "because of the little boy in me who used to play soldiers." His output is exhausting: he's already shot most of Star Wars: Episode 2 in between filming Moulin Rouge. Next up is Young Adam, closely based on the Alexander Trocchi novel. "It's a really sexy, erotic, dark, anti-society movie. It's wicked." He pauses. "I don't say wicked ever. I'm turning into the Naked Chef…ha! The Naked Actor!" We're no strangers to the actor naked. The McGregor manhood has had starring roles in, among others, The Pillow Book-in which his member was described pantingly by one woman's magazine as "incredibly handsome' -and Velvet Goldmine, Todd Haynes's paean to the glam rock scene.

When he was making Velvet Godlmine, he says, he had a serious fanaticism about Oasis, "like you should do when you're about 15 or 16 but I never did as a teenager. I had it for Oasis when I was about 15, married with a kid, and I suddenly went into this big one about Oasis and met them and went really girly." He remembers watching The White Room and Liam hadn't turned up, so they did the first set without him. "I could imagine him at some party, surrounded by women and misbehaving, then suddenly remember he should be on The White Room and getting in a cab-getting in a cab-jumping in the back on his Mercedes and getting down there for the second set. They were living out my rock'n'roll fantasies, I thought…" He wanted to be Noel in the Be Here Now video when they're playing Maine Road and he comes out in front of the Manchester crowd and just stands there with arms raised. "***** hell, I watched it over and over."

So when he was offered Velvet Goldmine, he said he'd only play rock god Kurt Wild if they let him do all his singing live: "I just wanted to feel that. I of course imagined 25,000 people in the stadum. We had about 400 in Brixton Academy, but they moved them around, and I kind of got the idea." He recalls ploughing through a few Stellas before going on, but the experience stays with him. "It did kind of help me get over the rock star hump a bit, because I felt I'd done it a wee bit." Baz Luhrmann has said that in the singing stakes, Ewan's up there with Bono. Andrew Ross, McGregor's singing coach for Moulin Rouge says he has what it takes to be the next David Bowie. So when can we expect your first album?

"It can be very cheesy, can't it?" he says. But does he want to carry on working with Marius de Vries, who did all the Moulin Rouge music and produces Massive Attack and Bjork. "I'm a bit frightened of the record company thing because all I've heard are nightmare stories. So I'm going to naively carry on untile I've got something that's ours and flog it." In the meantime he's going to take lessons for the five-string banjo his wife gave him as a "wicked" Christmas present. "I've been playing guitar at the same standard since I was 14 and never managed to get any better."

He used to play French horn, blows the trumpet occasionally, and now he's teaching his five-year-old daughter Clara to play the harmonica. "Totally **** awesome!" screams Ewan McGregor as he removes his helmet and gauntlets and shuts off the rasping 1,000cc engine of the Fireblade. He has come through unscathed, and we are saved from being involved in writing off one of Britain's best. Being and actor so informs his personality that when he's explaining things, he really, really wants you to share the experience. "There's nothing like riding on a race track. Riding the roads is great, but- I can't describe it to you- on a track like Brands Hatch it becomes a much more technical exercise.

You know nothing's coming the other way and you know if you come off there's a long way to slide and you'll be fine. It's a brilliant, brilliant feeling going round with the tarmac coming round your helmet as you corner." You get the feeling that Ewan's glass is never half-full: it's overflowing, with plenty left in the bottle. These days, it's more likely to be mineral water than Scotch. But he's still chasing the craic.

With all the pent-up enthusiasm of a kid about to go to a theme park, Ewan couldn't wait to pick up his new bike the evening before so he could thunder down to Brands Hatch. "I love bikes, I can't tell you, " he says. "I've got a Ducati, a Suzuki Bandit 1200 and a beautiful old Moto Guzzi 1978 race bike." In Moulin Rouge, Christian's journey takes him through hell, to emerge on the other side able to live and love properly. Ewan's been down this road: "I think it happens to everybody- it certainly happened to me." He recently turned 30 and now has a second child on the way.

"I realise more and more that's everything. I was a bit of a headcase for a while. I think there's a craziness I got out of my system. I use to spend a lot of time not being at home, in bars and stuff. Then I realized I didn't want to be in Soho with a bunch of people I didn't really know. I don't know if it has to do with being older, but I have never felt happier just being at home. It's more important than anything else, and I've never felt it more than I do now every morning when I wake up."

Pausing between circuits at Brands Hatch, McGregor, looking very Steve McQueen with a Marlboro wedged between his lips, reclines in the pit lane being photographed. The track's safety car pulls up. " I know you're the destroyer of the dark forces, " the official calls out good-naturedly, "but even you're not allowed to smoke in the pit." McGregor's the man men want to be mates with. This quality, this man-of-the-people aura that belies his celebrity status, is what everyone responds to.

He's been voted the third most powerful man in Scotland. He's just been handed and honorary doctorate from the University of Ulster. He's Britain's Johnny Depp. After completing his final roar round the track, he discovers that when he arrives in New York the next day for a round of TV chat shows to promote Moulin Rouge, there will be some Helmut Lang clothes waiting for him at the hotel. He can't resist it. "It's **** great being me!" Dr Ewan McGregor whoops. Yeahyeahyeah.