My biggest role? Being a dad

For an actor who has convincingly played such powerful figures as Tony Blair, Henry V and Mozart, Michael Sheen is almost perversely unassuming. The bright, animated face that looks out from a nest of corkscrew curls is wide open and friendly, free from the twitches of arrogance that might be forgiven in a man described by more than one critic as "the most exciting actor of his generation".

I meet him in the relaxed Saturday brunch atmosphere of Soho House, in a room filled with London's bright young things, blearily contemplating the weekend over a latte. Sheen has flown in from Los Angeles the day before, yet astonishingly looks much more alert than those simply recovering from the rigours of a glamorous Friday night out.

"I've visited most major cities in the world now, and there's still nowhere that excites me as much as London," he declares.

Given his last extended stay here during the summer, that is not too surprising: for five weeks he was filming Channel 4's drama The Deal during the day, in which he played Tony Blair, and then being taken by motorbike to the Donmar Warehouse to appear as the decadent Caligula in the evening.

Yet such traffic-dodging escapades aside, Sheen has far simpler ideas about why he prefers the dubious pleasures of a rainy day in London to the blue skies of California. "When I'm in LA, there are all kinds of things I miss about being here: walking around and seeing the fabulous architecture and bumping into people I know. I'm still in the process of coping with Los Angeles, but I'm trying to create a life there because that way I can be with my daughter, Lily, all the time."

Tabloid hounds cannot fail to be aware that while Sheen's talents have been on display on both sides of the Atlantic during 2003 (in such roles as the "naughty salt"-sniffing Miles in Stephen Fry's Bright Young Things or as a werewolf in Len Wiseman's Underworld), it has also been the year of his very public split with the actress Kate Beckinsale; they had been together for eight years.

Numerous articles have chronicled the horrible irony that while he and his long-term girlfriend were acting together in Underworld - a script that Beckinsale almost passed up - she and director Wiseman were discovering a chemistry that ended her relationship with Sheen.

In June, Beckinsale, now 30, and Wiseman got engaged - Sheen magnanimously says of Wiseman, "He seems a nice guy" - yet Sheen and Beckinsale seem to be on very amicable terms, not least because of their four-year-old daughter. At the time, he said there was "lots of hurt and mess, but you have to sort that out fast when there's a child".

"We all get on," he confirms now. "I think Lily is a real mixture of me and Kate. Everyone says that facially she looks like me, and she's also quite wicked. She definitely has Kate's wicked sense of humour."

Lily features constantly in Sheen's conversation, and it comes across strongly that fatherhood was an important wake-up call to the fact that there was a world outside the theatre (he even met Beckinsale on a production of The Seagull).

"In a sense, I grew up on stage," he laughs, "and, during my twenties, acting took over. I didn't need a base, didn't need much money - I was just doing what I loved doing and that was enough. But after a certain amount of time, I started getting very tired and felt that there was nothing else going on in life. Lily's birth was one of the things that changed that."

To be close to Lily, Sheen has decided to live 10 minutes away from Beckinsale in Santa Monica, a place he also likes because its closeness to the sea reminds him of his childhood in Port Talbot.

"My family lived on top of a mountain," he says proudly, "in this extraordinary place that combined the sea and the countryside with an incredibly ugly industrial town."

He is still very close to his parents; his father, who works in personnel, pursues an enthusiastic sideline as a Jack Nicholson impersonator. His mother, now retired from personnel, shares his father's additional enthusiasm for amateur operatics, and Sheen relates their delight that his cousin, Caroline Sheen, is playing Truly Scrumptious in the West End's Chitty Chitty Bang Bang, "so she's fulfilled all those musical dreams for them".

It is striking that the hyperventilating reviews that have greeted Sheen's appearances on stage echo the excited responses to another famous boy who grew up around Port Talbot - Richard Burton, who won the Evening Standard Best Actor Award in 1955.

"Watching the white-hot performance of Michael Sheen, you start to appreciate the derivation of the term star," raved the notoriously difficult-to-please New York Times in 1999 when he starred on Broadway in Amadeus. "Michael Sheen will blaze in the firmament for years to come. This brilliant young actor was a definitive Jimmy Porter four years ago in Manchester and last night recreated, and even improved upon, that memorable performance..." cried the Daily Mail, again in 1999.

Coincidentally, also like Burton, Sheen was initially tempted to pursue a career in sport, but while Burton was passionate about rugby, Sheen's great love was football. "I was offered a place on the Arsenal youth team when I was 12," he reveals with a shy smile.

Arsene Wenger's loss has definitely been theatre's gain. And Sheen is in no doubt that one of his favourite roles during his career has been playing the power-crazed emperor in Camus's Caligula this summer. At the Donmar he gave a performance that The Independent described as "one of the most thrilling and searching... I have ever witnessed".

It is little surprise to those who have watched his career that Sheen has been seen worthy to compete with actors of the calibre of Kenneth Branagh and Warren Mitchell for this year's Evening Standard Best Actor Award.

At the age of 35, Sheen can now more or less pick and choose his roles. However, it seems that much of his future will be spent in Hollywood, given his determination to remain close to Beckinsale for their daughter's sake.

"Kate and I see each other all the time - our relationship together is important, not just for Lily but for us. I think Kate enjoys the LA lifestyle more than me, and it makes sense for her to be there because she's doing more and more film work.

"There is a lot of pressure to subscribe to the celebrity culture, all that stuff about who's the best-dressed and who's the worst-dressed in magazines is palpably lighthearted but if you don't go along with that, certain things won't be open to you.

"That's something that Kate wants to do, but as a man it's easier for me to say I'm not so worried about it."

Doors certainly don't seem to be closing as a result for Sheen: next year he will be working on Ridley Scott's new film about the crusades, starring in a movie about Dylan Thomas and taking Caligula to Broadway. Does he have any dream roles that he hasn't played?

"I've just seen a documentary about Bobby Kennedy, and it strikes me that he was a genuine hero who was much more radical even than his brother JFK. Now there isn't a play about him yet, but if someone was going to write one...." And his eyes gleam.