In a Soho record shop, Alfie Allen flicks through the racks of vinyl with nimble fingers. He picks out punk-era favourites such as Gang of Four and the Slits and laments the store's lack of dance ("I'm really into house right now"). He happily apes poses from album covers for our photographer, recreating everything from Grace Jones's contortion on Island Life to hip-hop producer Marley Marl's cocky pilot on In Control. Alfie just shrugs at the chortles from his audience of shop assistants, publicists and even his own agent. "I really don't mind what I do," he says with an affable grin.

The 23-year-old actor does seem very self-possessed. Lucky, really, as he must suffer from being seen as son of Keith Allen and brother of Lily. But this autumn should establish him as a star in his own right. First up is SoulBoy, a film set in the 70s northern soul scene. After that, he's in The Kid, based on Kevin Lewis's bestselling autobiography, as school bully Dominic. "Kevin found it hard to talk to me after he saw my scenes because he hated that boy so much. I hope that means I did a good job. Though I've done a few bullies – maybe I've just got a bully's face. I do prefer playing baddies because you can push being horrible as far as you want."

After Jimmy McGovern's new BBC series, Accused, there's the role of Theon Greyjoy in Game of Thrones, the eagerly awaited HBO adaptation of George RR Martin's fantasy novels, which have sold 7m copies worldwide. "Theon's a bit of a wrong 'un, too," Alfie cheerfully admits. "Game of Thrones is my big break so I've got to make the most of it, keep acting well."

He obviously loves to act. As we talk, he drops into different characters so easily it's unnerving. Alfie almost disappears. Instead, he's a cockney, a Belfast local; at one point, he's Peter Capaldi and at another Aidan Gillen. He looks bashful when I compliment him on his way with an accent. "I do take pride in them. I think it's a gene thing. My dad's good at them and Lily's amazing – she does a brilliant Cheryl Cole."

Is he nervous about all that lies ahead? "I actually love pressure. I loved playing sport at school in front of a crowd; I love being on stage in front of a big audience. I buzz off that." He shrugs. "And if it goes tits up, then it's on to the next thing."