Hey, good looking

Robert Sheehan nearly blew it when he met Kevin Spacey.

To be fair, he has a right to feel just a little bit chuffed. The 23-year-old policeman's son from Portlaoise in Ireland arrived in London four years ago, breezed into the smartest TV teen drama of the past few years and is about to star in one of the great Irish plays - JM Synge's The Playboy of the Western World. As Christy Mahon, the title role, he carries the show on his slender shoulders, delivering great rolling phrases of poetry and imagination that still sound fresh more than 100 years since they caused riots on the streets of Dublin. 'The lovely thing about this part is that he completely transforms from a milky soft little snivelling creature who confesses he's just killed his father to this alpha-male peacock as the play goes on.' Sheehan gives a wicked grin. 'Or at least that's what I'm going to attempt to do with it.'

Christy is a bad boy made vulnerable and Sheehan's career has been all about that sort of boy. Nathan in Misfits - who has an online-only episode honouring his recent departure currently playing on 4oD - was a cheeky, reckless, charming little thief, who also happened to be immortal; Luke in 2009's Cherrybomb (also starring Rupert Grint) was a drug dealer; BJ in gritty Channel 4 drama Red Riding was a male hooker with a heart of gold; while Kay, the altar boy turned knight in Nicolas Cage's epic Season of the Witch, just kept killing people by accident.

'When I was a kid I was relatively well-behaved.' He gives a slow grin. 'But I have been a bit of a scamp in the past. I mean, young fellows being young fellows, they get into scraps and trouble every once in a while, but I've never been arrested. I remember a big, organised fight when I was about 13 on a green near where I lived. It was weird, it was like: choose a side, you're on one side or the other. There were guys in cars with the stereos going and all of a sudden a cop car drove up and my dad got out and yelled, "Robert!" and I went, "I'm sorry, I'm sorry, I'm sorry," and got the hell out of there. That was the nearest I got to Dad putting the cuffs on me.'

Having cast off his Misfits hoodie, Sheehan loved modelling the latest menswear trends for ES. 'I particularly liked the Boardwalk Empire look: this big, old Dean Martin-style trench coat over the shoulders; long, baggy slacks with the slip shoes and the hat, and their hair all slicked back that was a favourite.' Although he's not quite at the Alexa Chung level of fashion muse, stylists already love him. He's got the wild black curly hair and piercing eyes of the South of Ireland - where the Armada was wrecked and Spanish blood mixed with the Celtic, to double the passion and the laidback ways in equal measure. As a result, unlike his freckled redhead compatriots, he tans deeply, returning from Thailand and Cambodia last spring looking nut-brown and causing considerable excitement among London's gentlewomen - Google 'Robert Sheehan gorgeous' and see.

The photographer Pierre Debusschere was so impressed he chose Sheehan to model Dolce & Gabbana's S/S 2010 collection in a short film celebrating 20 years of the label. Sheehan confides that he also managed to wangle two suits out of Louis Vuitton as personal gifts. 'It's like finding a fiver in a pocket just before the wash and going, "Yes, bonus!" ' he says. 'I'm interested in clothes but sometimes I come in looking like a militant lesbian and then other days a vegan from the 1960s who just fell out of Woodstock.'

He spent a few years avoiding his trademark curls, shaving his head or straightening them out with tongs. He did Rock Rivals, a drama based on The X Factor, for ITV, where he was the lead singer in a boy band sporting dead-straight Japanimation locks. 'Nowadays,' he sniggers, aping a haircare ad as he tousles his locks, 'I just let it run wild and free.'

He came to London after meeting a riding trainer on the set of Season of the Witch and moved into her flat. 'We're not still together but strangely enough we're still friends.' He stops, aghast at what he's just said. 'Not that we fought badly or anything, it's just that it's hard to stay friends with your exes. She lives such a strange and wonderful and nomadic life. She has her own stunt riding team called Blazing Saddles and they do the most amazing shows around the UK and in Ireland. Every time I talk to her she's got a sprained elbow or a bruised spine.'

He's not dating anyone specific at the moment, just 'casually flitting round London town', going to Soho House with his actor friends Douglas Booth and Freddie Fox, enjoying the thrill of being 23 in the greatest city on earth. Friends from Dublin are drifting over - two more arrived just two days before our interview - but he also knows a crop of YBAs (Young British Actors) including Tom Hiddleston and Ben Barnes. He goes drinking with the current cast of Juno and the Paycock at the National and likes a spot of karaoke at The Dolphin on Mare Street: 'My singing voice is terrible and gets worse the drunker I get. I do like a bit of 'Come On Eileen', though'

For now, it's definitely Mare Street and not Sunset Strip for our boy. 'Tom [Hiddleston] had to put on so much muscle for Thor,' he says, staring down at his own slender frame. 'He went from my size to close to Chris Hemsworth's in four months. He hired a personal trainer, he did all the protein stunning dedication. I just don't think I'm prepared to go out there and do all that work just at the moment. Never say never, but I just live on pasties. There's a pasty shop right opposite The Old Vic and I go down there every second day.'

But Hollywood is sure to come calling now that Misfits is a hit in the US. He admits it's a beautiful place: 'Every-body eats giant sandwiches and plays volleyball, but I don't want to live in an episode of Entourage just yet. My agent over there said, "If you want to know what we do, watch Entourage," and I said, "You should get a different f***ing job, mate." ' ES
The Playboy of the Western World is at The Old Vic from tomorrow until 26 November (0844 871 7628; oldvictheatre.com)