Jason Priestley, arriving late but not rudely late to the suite he has booked in a New York hotel, knocks politely and enters just as Tom, the photographer, is cursing his unluckiness in love. "Tell me about it," says Priestley, in an I'm-no-stranger-to-heartbreak way. And this Tom does.

There is an easiness about Priestley, best known for his heroic eight-year, 278-episode stint as Brandon Walsh in the TV show, Beverly Hills 90210, that encourages a trade of intimacies. I could hardly have less in common with this teen heart-throb and his passion for rally driving, hockey and a band called BareNaked Ladies, but we are soon getting on like old friends. Indeed, Priestley, rather mysteriously, seems to think we are old friends. "We've done this before a couple of times," he assures me at one point. I wonder, briefly, if he thinks I've interviewed him in another life or something. "Never?" he queries. "I'd swear to God! I guess all Limeys look the same."

His affability encourages me. I'd been prepared to meet an ego bruised not only from the indignity of fame won from an Aaron Spelling soap but by his personal life, whose vicissitudes make Tom's look halcyon. Late last year, Jason separated from his wife, Ashlee Peterson, a make-up artist, after only 10 months' marriage. The same week he crashed his car and was charged with drunk driving. The only good news has been professional. Having finally escaped 90210, which, without him, seems finally to be limping to the knacker's yard, he has made Eye of the Beholder, a proper, grown-up thriller starring Ewan McGregor, opening on Friday in America. Next month, he arrives in London to star in Side Man, a literate, downbeat examination of dissolute jazz musicians which won a Tony Award on Broadway. In the trend to import Hollywood stars to the West End, he follows Nicole Kidman and precedes Kathleen Turner, who arrives in the spring with a stage version of The Graduate. It is not quite as unlikely as Richard Chamberlain starring in Hamlet after years playing Dr Kildare but any Priestley fan expecting Grease meets Melrose Place is in for a disappointment.

"Yeah, I got married in January," he agrees. "Unfortunately that didn't work out for me. It was unfortunate. She is, you know, a wonderful woman and I talk to her all the time. We're still good friends, thankfully."

He brightens. "It's amazing, you know, how many people I talk to who say, 'Oh, yeah, I was married for a year once.'"

Jason and Ashlee had been friends for some time, but it took them only six months to realise they should never have married. "Like: maybe we shouldn't do this! And it's better than slogging it out for five years and then hating the person. It's better to talk about things, the problems you are having in a relationship and realise that maybe some of them are insurmountable. I think we have all been in relationships we think we can make work and five years on realise you've just wasted five years of your life. Life is short. Life is precious. I guess as you get into your thirties you really start to grapple with your mortality."

It is, I admit, slightly bizarre grappling mortality with America's best-known high-school kid, but I'm the last person to hold Priestley's Dorian Gray appearance against him. When 90210 debuted on Fox in 1990, Brandon was beginning his junior year at West Beverly Hills High, but Priestley was already 21. To take nothing from his performance, which had a graceful irony to it, his genes helped. He not only looked younger than he was, he was short, 5ft 7in tops. The British comparison would be with Roger Tonge, a conveniently tiny actor brought in as Meg Richardson's son Sandy when Crossroads started, but whose height eventually tolled so heavily against him that he was consigned to a wheelchair to disguise his stature.

Today, the perfectly formed Priestley is sporting a neatly trimmed auburn beard. Although visually this takes him slightly nearer his 30 years, he still speaks as if he is at West Beverly: he digs things, man and they are cool. His vocabulary suggests wariness around emotion. He calls Side Man's searing treatment of alcoholism "touchy, emotional stuff" - which seems a touch inadequate.

I say it must be a relief to be playing Clifford - someone his own age, at last. "I'm an adult now. I'm 30. I have to behave like an adult and start portraying adults. I don't look 21 any more. I look in the mirror and see a 30-year-old man. I'm very happy about that, actually. I'm very comfortable in my own skin, which is good, a good place to be. I wasn't for a long time. You know, in your twenties, you are trying to figure out who you are and what you believe in."

The figuring out was hampered by the media attention? "It's really hard getting through your twenties, when you are living in a goldfish bowl. It can be very trying. I'm just glad I survived it. LA is one of those town where everyone's always watching everybody else. The last time I checked, you are supposed to make mistakes in your twenties, learn from them and then move on. But if you are on a television show, everyone is watching and those mistakes become bigger than they really were."

What kind of mistakes did he make? "Personal ones, professional ones. The most important thing is you learn from them. If you continue to make the mistakes then that's a problem." He does not, however, consider staying so long on 90210 a misjudgement.

He produced on the show, directed 20 episodes and has subsequently directed a TV movie and a documentary about the aforementioned BareNaked Ladies. Since his clippings file contains no tales of brat-pack misdemeanour either, I suppose the mistakes he refers to are romantic ones. He has tended to live with his girlfriends, first Holly Robinson from 21 Jump Street, and then for five years with ER actress Chris Elise. But perhaps these are not the errors he is referring to either. If Holly, Christine and Robyn Lively (from Teen Witch, whom he also dated) were mistakes, he obviously repeated them writ large with Ashlee.

Gallingly, Jason was always being compared with his character, Brandon, America's perfect son. Like Priestley, Brandon Walsh arrived in Los Angeles from Nowheresville (Canada in Jason's case, Minneapolis in the Walsh family's), immune to LA's excesses and neuroses. In a characteristic episode, such as the one Channel 5 showed on Sunday, Brandon tackled a fashionable social problem - the athletic team's reliance on steroids - and cured it. It was somehow typical that just before Brandon left the show in 1998, he too ducked out of a marriage, but on the morning of the wedding rather than 10 months after it. "If I could make decisions like Brandon," Priestley sighs, "I'd be in a much better place."

But Priestley, who pretty much defines wilful American optimism, sees a positive side even to this confusion. "In a play like Side Man, it's almost good to have some baggage. The audience goes, 'Oh yeah, I know this guy', which is kind of cool, because you need the audience to go along with Clifford. I suppose what I'm saying is it's good that my old TV show is on BskyB."

What he is implying, however, is that his success in Love and Death on Long Island two years ago failed to purge Brandon. In this excellent film, John Hurt, as a repressed English professor, chances upon a terrible frat-house movie and falls in love with it's lead, Ronnie Bostock. Priestley played Ronnie, star of Hotpants College II, as a simple-minded version of himself. To put it another way, Priestley played dumb uncannily well. As he says: "It's a fine line, you know it really is, between playing bad acting and just bad acting."

How skilful an actor Priestley actually is it is hard to tell. His boldest movie was Coldblooded, a 1995 black comedy about a reluctant Mafia hit man. It is especially difficult to assess Priestley's performance in this since he chose to play Cosmo almost autistically. As his victim's blood splashed his unresponsive face, Priestley, you realised, had stopped acting altogether.

Priestley compares Side Man to Jeffrey Bernard Is Unwell, not only because it deals with debauchery but because the lead character also narrates it. To me it is more reminiscent of Thornton Wilder's Our Town, in that its real subject is a childhood seen from the adult's perspective. Jason is reluctant to say what he will bring to it from his own upbringing in Vancouver, pointing out that while he chose his profession, his parents have not volunteered to be public figures. His father is a businessman and his mother once danced with the Royal Winnipeg Ballet, but he will not tell me their names. What we do know was that he made his first TV movie at eight. But he denies that his mother pushed him into his career or that he sacrificed his childhood for it.

So, while Clifford's childhood in the play is disastrous, his own was happy? "Absolutely. I had a wonderful …" But here he stumbles. "I had a normal childhood. Put it that way. I didn't grow up in a Norman Rockwell painting either.

"It's a fine line between playing bad acting and just bad acting".

Are his parents still together? "Oh no, my family is as disjointed as anybody else's. I would venture to say I had a very normal childhood, and a very normal upbringing. I mean, hell, it was the Seventies!"

Jason's insistence on his representative normality is heartfelt. He claims he still has a mortgage - "it's the one tax-deductible I have left" (his ex-wife, presumably, was the other) - and says he would hate to travel with an entourage. When I tell him he has his own website, he is astonished.

It is, of course, buzzing with the latest scandals. "Getting separated from your wife just isn't the end of the world," he says, "but all of a sudden I am back in the media again. And I am just not one of those guys who likes to be in the tabloids. I really don't like it, actually. I like normalcy, a nice, quiet existence. I'm not a monk. I like to have a private life, but not to lead it in front of the media."

The net gossip about his marriage was quickly followed by the car smash headlines. With court proceedings imminent, he says be cannot talk about it, but it was reported that, driving home from a concert, he crashed his new Porsche. The sports car hit a dustbin, a parked car and "several fixed objects". His male passenger broke his arm. A blood-test showed Priestley was over the California alcohol limit. He is pleading not guilty to a charge of driving under the influence, which could, in theory, carry a three-year prison sentence. He says he swerved to avoid a deer.

So, he will be in London playing Side Man (previews start at the Apollo on 17 February) on $50,000 bail. I'll be fascinated to see how he does, if he manages, for a start, not to be outclassed by the wonderful Edie Falco, Carmela from The Sopranos, who plays his mother. He has not acted on stage for a decade - "and that was a strange, avant-garde thing in Vancouver: a hula hoop, no clothes, a 60 seat theatre."

I hope he copes. If not - or even if he does - he is not so precious that he would necessarily turn down another TV series. Having had fun meeting him, I think he'd be excellent in a sit-com. His favourite line from Side Man is a Proustian wisecrack about returning to the "zip code" of his youth.

The escapee from zip code 90210 laughs a lot at that one.