With his bulky frame and mellifluous voice, Roger Allam was made for villainy. You may have seen him over Christmas as a gleefully cackling Abbanazar opposite Ian McKellen's Widow Twankey in Aladdin. And you can catch him as the embodiment of a fascist future Britain in the Wachowski brothers' forthcoming thriller V for Vendetta.

   Panto and a Hollywood blockbuster from the makers of The Matrix? That's typical of Allam's varied CV, but the idea of evil is disturbingly blurred for his new stage role. In David Harrower's tense drama Blackbird, acclaimed at the Edinburgh Festival last year and now opening in the West End, Allam is fiftysomething Ray, who is confronted by Una (Jodhi May), a 27-year-old woman full of unanswered questions regarding their sexual affair when she was 12.

   "These are two very damaged people who were consumed by desire, but in no way is this a defence of paedophilia," stresses the 52-year-old Allam. "Ray was undoubtedly wrong and was jailed for his actions. But the play is really about the shockwaves of such a relationship. It's the most overwhelming thing that has ever happened to them."

   In its exploration of self- delusion and personal responsibility, the play is drenched in ambiguities as Ray and Una wrestle over the meaning of their past. "It's fascinating to tackle a play like this," Allam says. "The dialogue is sometimes fractured, almost like poetry, and people aren't saying, or are unable to say, what they mean."

   Blackbird also offered Allam the chance to work with Peter Stein, the German maverick who was the formative artistic director of the Berlin Schaubühne company in the Seventies and Eighties.

"No other director I've worked with combines such a marvellous visual sense and a forensic analysis of the text with an awareness of body language," he says. "In this play they say one thing but their bodies can say something else."

   Working with Stein also meant rehearsing at the director's country estate in Umbria. "It was bizarre reading up on paedophilia in such lovely surroundings," Allam says. "The estate has olive trees and wild boar. But it got very hot and there's nowhere else really to go, so rehearsals were pretty intense."

   The part of Ray adds to Allam's impressive range that encompasses Benedict in Much Ado About Nothing, a Chandler-like private eye in the musical City of Angels, and starring opposite Gillian Anderson in the West End two-hander What the Night is For. He's even played two German Chancellors: Adolf Hitler in David Edgar's Speer and Willy Brandt in Michael Frayn's Democracy.

   Such versatility comes at a price. Having been a stalwart of the Royal Shakespeare Company in the Eighties and the National in the Nineties, he's now one of those actors who regular theatregoers know will deliver something funny, fresh or true. But he's yet to have the screen break - ie, a hit detective series - that makes you a household name.

   His film parts have been small - he describes his V for Vendetta role as "this fascist evangelist TV presenter, a tiny but fun turn" - and admits that people aren't sure how to cast him. "Nowadays, especially in film and TV, you have to cultivate a distinctive persona," says Allam, whose desire to be an actor was first stirred by a recording of Paul Scofield as Lear.

"I belong to an older tradition that encouraged you to be as versatile as possible. I remember seeing this book at school about Olivier, Gielgud and the like. It had all these pictures from their rep days in all sorts of roles. That's what acting is all about, I thought."

   The son of a London vicar, Allam can recall "playing on the bomb sites in the East End in the Fifties". A good enough singer to play Javert in the original production of Les Misérables, he was encouraged to become an opera singer but opted to study drama at Manchester University: "I realised you could do a lot more as a young actor than as a young singer."

   His first job was as part of the feminist troupe Monstrous Regiment in the Seventies: "I could sing, play piano, keyboards and guitar, which suited a collective where you did everything. One day I'd be handling the lights, the next discussing a new play with Caryl Churchill."

   Last year he became a father for the second time. He and his actress wife Rebecca Saire now have two sons, William and Thomas. And after years of being a company man, he now wants to keep himself "open to possibilities". He doesn't know what lies beyond Blackbird. But he's keen to tackle Lear. "After all," he says, "it's what made me want to act in the first place."