THERE'S something about Alfie Allen that reminds me of a young Mick Jagger.

He's not what you'd call handsome exactly, but he has a beguiling air of self-assurance that stops short of arrogance. It's something that comes from knowing that you're good at what you do. And Allen is very good.

His powerful performance as Alan Strang, the troubled teenager with a disturbing fixation for horses in Equus, is all the more remarkable given the fact that he's a theatrical novice. David Niven once admitted that he suffered so badly from nerves before going on stage that he was sometimes sick in the wings, so what must it be like for a 21 year-old playing the lead in a high-profile play?

"It was nerve-wracking on the first night but I've got a habit of not letting nerves get to me. Even when I was younger at school and we used to play big football matches, I always seemed to rise to the occasion."

He had the somewhat daunting task of following in the footsteps of Harry Potter, aka Daniel Radcliffe, who won plaudits for his performance as Strang in the West End last year. Surely that made him nervous? "Nah, there was no added pressure but I was happy when the producer said he wanted it to be a completely different production to the one Daniel did."

He didn't go and watch Radcliffe's performance and admits he knew little about the play before he was cast. "I'd heard of Equus and I knew it was about horses, but I didn't know much about Alan Strang."

There is a strong chemistry between himself and Callow on stage, something that's crucial to the play's success. "When you're working alongside people like Simon Callow who makes you feel relaxed, and when you know everyone's got faith in you, then that just makes you want to do it more and more."

For Allen, acting was always going to be a likely career path. His father, Keith, is an actor and comedian, while his sister, Lily, is a chart-topping singer and TV presenter. "I can't say whether it's been a help or a hindrance because I just focus on what I'm doing," he says of his family connections.

"Acting was always there. My dad would do role playing in front of his friends, he'd do silly accents and characters would be just jumping out of him. It was only later that I thought it might be something I could do."

He takes his clothes off every night in Equus, something most of us wouldn't have the bottle to do.

"After the first time you get over it and keep on doing it and eventually you start enjoying it," he laughs.

Allen's acting career started almost by accident when he was 16. "I went to an audition with my mate for this film called Agent Cody Banks 2 and it just went from there."

Since then he's gone on to appear in Atonement, alongside Keira Knightley and James McAvoy, and has recently finished filming Flashbacks of a Fool, starring Daniel Craig. But he says he doesn't get starstruck. "I only get awestruck by footballers. When I met Thierry Henry I was like 'wow', but when I'm working with people it's like, 'you're that guy off the telly' and when you meet them they're just normal." After Equus Allen is unlikely to be short of offers. "I'm probably going to have the luxury of choosing what I do next, but I haven't got a grand plan I'll just go with the flow."