IT'S JUST as well that the bar of the theatre where I'm due to meet David Suchet is almost empty, because I realise, to my embarrassment, that I haven't a clue what this most distinguished of character actors looks like. But then, who does?

The real Suchet, by contrast, turns out to be diffident, gracious, ineffably charming and shockingly ordinary. Once likened to a "Levantine secret policeman", the stocky 50-year-old is probably the only award-winning television star who could walk down a crowded street unnoticed. Which goes a long way to explaining his brilliance and versatility as a character actor. "Many actors are cast because of who they are," says Suchet. "But people cast me because of who I'm not."

Today, he's partly disguised by a late-Fifties suit and a pair of bulky spectacles, through which his velvety brown eyes gaze with mesmerising intensity. His voice - almost unknown to a public accustomed to all those thick foreign accents - is rich, fruity and exquisitely modulated. He has been rehearsing the part of George, the caustic, embittered academic in Edward Albee's Who's Afraid of Virginia Woolf?, which opens tomorrow at the Almeida Theatre in Islington, London.

"This is a better role than the one in Oleanna, because it has far more dimensions," he says. "There are so many layers to George - intellect, humour, wit, disillusionment, sarcasm, rage, pain, need. He's beautifully written and drawn very clearly. The challenge is to bring it off the page into me." Although he is familiar with the ways of academe, having spent a year as Visiting Professor of Theatre at the University of Nebraska (where he knows of an academic "so like George it's unbelievable"), he reckons that this may prove his trickiest role yet. He likes to make a list of all the things he has in common with the characters he's playing: the one for George is his shortest since Caliban.

It's an unusually showy piece of casting for Suchet. Apart from Oleanna and What a Performance (in which he shone as Forties variety artist Sid Field), his theatre work has traditionally been confined to the great supporting roles such as Shylock, Bolingbroke, Caliban and Iago. But he has never sought the centre stage. "I'm not interested in turning a role into a star performance. I don't care about anything but the truth of the character I'm playing."

He ascribes this punctiliousness to the influence of his father, a Harley Street specialist. "Because he never wanted me to become an actor, I wanted to prove that it could be a very honourable profession. I didn't see it as a place where I could have a good time or become a star. I wanted more than anything else to be respected for the truth and complexity of the work I was able to do."

Suchet's was widely considered the definitive Poirot, because, typically, he immersed himself in the character

It is an approach which might have kept him in critically-respected obscurity to this day, had it not been for the vast success of Poirot. In its six-year run, the series brought him 100 fan letters a week, won him three Bafta awards in a row and made him enough money to buy the rambling family home he shares in Middlesex with his wife of more than 20 years, former actress Sheila Ferris, and their children, Katharine, 13, and Robert, 15.

Suchet agrees that Poirot was a middlebrow confection and that the character was a "cardboard cut-out", but says he would still leap at the chance to play the detective again - preferably on film. "He had a lot of personality defects and eccentricities which coloured him for me so that I could make a fully rounded character out of him." The Albert Finney and Peter Ustinov screen portrayals of Poirot may have been flashier, because they stamped their ebullient personalities on the role. But Suchet's was widely considered the definitive Poirot, because, typically, he immersed himself in the character. He ploughed gamely through the complete works of Agatha Christie in search of salient details; and he often remained in character when not filming - doing that mincing walk, speaking in a prissy Belgian accent and, before each scene, fastidiously measuring the amount of cuff showing beneath his jacket.

His research for a six-part BBC series on the life of Sigmund Freud was similarly thorough. "I went to Vienna; I studied with the Freudian Analytical Society; I read everything he ever wrote; I was taught his technique of psychoanalysis; I met people who knew him, including an old lady who lived below him in the 1930s; I read around the work of contemporary psychiatrists like Reich and Adler to get him into perspective."

And in the case of Tom Kempinski's play Separation, he was even prepared to risk his health. Because Suchet was playing a writer who chainsmoked Marlboro, he took up smoking regularly - having quit the habit two years earlier because of a heart condition. It all smacks of that most unEnglish of concepts, Method acting. Suchet laughs when I remind him of that celebrated exchange between Laurence Olivier and Dustin Hoffman on the set of Marathon Man. Before filming a vital scene, Hoffman starts running hell-for-leather round the block. "What are you doing?" Olivier asks. Hoffman explains that he wants to look breathless and exhausted. "But, dear boy," says Olivier, "why don't you just act?"