Nora also marks his first film as a producer. He is credited as a co-producer on the film, and one of the production companies involved in making the film is Natural Nylon, which McGregor set up with his fellow actors, Jude Law, Sadie Frost, Jonny Lee Miller and Sean Pertwee, and producers Bradley Adams and Damon Bryant. Natural Nylon's projects biopics of Beatles manager Brian Epstein and playwright Christopher Marlowe and a film about the orgiastic Hellfire Club.
"Being involved with producing the film, I also feel very responsible for it," McGregor says of his dual association with Nora. "I've never had this much input into a movie before, and it's very much a labour of love. It's all just fantastic. For me, it's a real learning process in the way other films haven't been. Anything can happen. Film-making is full of ups and downs. We all know that, so you learn from that. I'm chuffed. It's a great start for our company. I'm really proud for Pat, too, because she's been working on this for eight years."
Given that every biopic is now subjected to the most minute examination to test historical accuracy, how does Ewan McGregor expect the legions of James Joyce purists to react to the film? "I just don't know," he says with a shrug of his shoulders. "I don't even know what people feel about him in this country. Of course, anyone who spends so much time on the same subject is sure to know much more about him. But I think it should be fine for them, too. It's based on what he wrote and the knowledge we have of what he was like and how he lived his life. It's Pat Murphy's representation of what she thinks he was like, and I've never met anyone who knows as much about him as she does. And if they don't like it, they can go off and make another one."
One of the most satisfying aspects of filming Nora, he says, has been working with his co-star, Susan Lynch. "She's brilliant," he says. "An amazing, amazing actress. An actress in the real sense of the word - not like some people who pretend to be actresses. She's wonderful to work with."
Ewan McGregor dates his own interest in acting back to when he was "about nine" and growing up in the small Scottish spa town of Crieff in Pertshire. His inspiration was his uncle, Denis Lawson, a stage and film actor who had a leading role in Local Hero - and, by coincidence, played the fighter pilot, Wedge, in the first three Star Wars films. "He always seemed very different to the other people I was surrounded by and at that age I wanted to be different, like him. So I decided to be an actor and I wouldn't let anyone sway me."
Having seen the first Star Wars when he was six, McGregor now has one of the starring roles in the prequel trilogy which begins with Episode 1: The Phantom Menace. He plays Obi-Wan Kenobi, who was played as an older man by Alec Guinness in the first series and who, as the new film begins, is the apprentice of the Jedi Master, Qui-Gon Jinn (Liam Neeson).
McGregor's dashing screen presence helps enliven the uneven, sometimes ponderously paced Phantom Menace. In his portrayal of Obi-Wan Kenobi, he sounds appropriately refined, given that that character already has been immortalised with such gravitas by Alec Guinness. "I've never met him and I just tried to get the flavour of him," says McGregor. "I watched a lot of his earlier movies, but at no point did I see the role as any kind of impersonation of him."
He sees the Star Wars series as "essentially a fairy tale about good versus evil" and he says that while he's looking forward to working on the next two movies in the series, he has no intention of restricting himself to Hollywood fare. "If you were to go over to Hollywood," he says, "and get stuck doing the same thing, doing big-budget American movies, you would never learn anything any more. I know how to do that now." Now 28, Ewan McGregor continues to be one of the busiest actors in the world. Already this year he enjoyed considerable acclaim for his London stage performance as a naive student revolutionary in David Halliwell's play, Little Malcolm and His Struggle Against the Eunuchs. He takes the role of the reckless Barings Bank trader, Nick Leeson, in Rogue Trader, which was released here a week before Leeson was released from a Singapore jail last weekend.
McGregor plays a surveillance agent in Eye of the Beholder, a thriller from Stephan Elliott, the Australian director of Priscilla, Queen of the Desert. The film, which opens here towards the end of the year, also features Ashley Judd, Jason Priestley and Patrick Bergin. McGregor's next project, Moulin Rouge, a musical to co-star Nicole Kidman, will be directed by another Australian filmmaker, Baz Luhrmann, who made Strictly Ballroom and Romeo and Juliet.
"He's mad, but he's a lovely man," he says of Luhrmann. "He's one of those film-makers any actor in the world would want to work with, isn't he? And it has also got singing and dancing in it, and that's something that's been a strand in my work since I started with Lip- stick On Your Collar. I've always been into music more than anything else, so it's a very natural thing for me to do."
Not content with diversifying by turning co-producer on Nora, McGregor recently made his debut as a director with one of the nine short films in Tube Tales, all of which were filmed on the London Underground. The other directors include Bob Hoskins, Jude Law, Armando Iannucci and Amy Jenkins. McGregor's episode, Bone, features one of his Little Malcolm colleagues, Nick Tennant, as a musician who invents a fantasy world surrounding the owner of a lost travel card displayed in the window of the ticket office.
McGregor's expression turns from his enthusiasm for that project to anger at the mention of several biographies of him which have been published in the past year. "I've never read any of them," he says dismissively. "I'm sure they're crap. It's scary. They call themselves `unauthorised' and they're allowed to do that! That's terrifying.
"They say they're doing a book about me and they want to interview me, and I say no because I don't want any books written about me. I think it's ridiculous. I'm only 28 years old. And even when I say no they're allowed to go and do it anyway. Behind my back, people I was at school with selling photographs of me. I think it's embarrassing."
Ewan McGregor has never been embarrassed about frontal nudity in his movies, as he showed in The Pillow Book, Trainspotting and Velvet Goldmine, but he says he's "thoroughly fed up" with the media's obsession with this aspect of his work.
"In one interview I read recently the writer referred to `the obligatory McGregor nude scene', and I was so offended," he says. "I thought, I'm really trying to do something with my work and it's reduced to some ignorant arsehole in a magazine saying something like that. It makes me so angry, because I'm worth much more than that. I'm trying to do something and it's not the obligatory McGregor nude scene. That's just nonsense.
"If I'm nude in a film, it's because that's what's required. I won't limit myself with anything. That would be like saying I won't walk down the pavement on the right-hand side because I don't do that. So why should I limit myself by saying I won't take my clothes off in a movie?"