"I've not been offered many parts," Derek Jacobi says wryly of his screen career to date. He thinks it's because he's hard to pigeonhole: neither conventionally heroic nor colourfully characterful, his pink, malleable features seem made for slipping into moulds.

Yet he has always been a star. Ever since his celebrated schoolboy Hamlet in 1957, he has been an actor's actor, rising steadily through the ranks of the subsidised theatre; then as the stammering tyrant in the BBC's 'I, Claudius', he became a household face on both sides of the Atlantic. But the limelight in which he is currently bathed--with a West End success and a Hollywood thriller which has just swept the board in America--denotes arrival of a very different order.

He took the title role in Jean Anouilh's cod-historical Becket almost by chance. Offered the choice, he wanted to play the king--"the part with the fireworks"--but persuasion from friends and the discovery that Robert Lindsay was set on wearing the crown led him to settle for what he claims is the hardest part he has ever done. "I'm a pyrotechnical kind of actor, but here I must work from a still centre, playing a man who doesn't know who or what he is. It's been a fascinating lesson. Every night it feels like starting from scratch." He plans to turn the table on Lindsay: when the show is properly run in, the pair will swap roles.

A greater degree of chance attended his incorporation into "Dead Again", Kenneth Branagh's stylish homage to Hitchcock and Welles. Donald Sutherland was originally hired to play the eccentric, antique-dealing hypnotist which is now Jacobi's part, but Sutherland and Branagh didn't hit it off. Solution? By scheduling the relevant scenes for a three-week gap in Jacobi's diary, Branagh managed to pull his old mate aboard. Co-starring Emma Thompson, "Dead Again" opens next week, and, though it's predicated on a piece of supernatural nonsense, it would be unfair to give away the plot. But one detail can be revealed: just before the gory climax, Jacobi's character suddenly redevelops the stammer which hypnosis had cured when he was a boy.

Sound familiar? Jacobi looks rueful, and for two good reasons. Claudius stammered, and so did one of Jacobi's most celebrated stage creations, the mathematician Alan Turing in 'Breaking the Code'. "I told Ken that it would look like a terrible professional in-joke and asked him to cut it. But he insisted on keeping it--he pointed out that it was there in the script, long before I was cast for the part." More seriously, the Association for Stammerers has taken exception to the film's implication that the disability can be cured by hypnosis. Jacobi thinks it is quite right to protest--"it might give a lot of people false hope"--and yesterday endorsed a round-robin letter which the association is issuing to the British Press. Research for the part consisted largely of bringing his own experience to bear: he used the technique 14 years ago to stop smoking. "My hypnotist had a soporific, melodic, sleeping-pill sort of voice, very relaxing and comforting. That's what I tried to recreate in the film."

This was his first job in big-time Hollywood, and he looks back on it with detached amusement, "Sweeping through the gates of Paramount on my first day in a stretch limo seems to have fulfilled a fantasy of mine." He wasn't so amused when it came to the stunts. "We had two stuntmen for the fights, but when they put on their hairpieces--a blond one for me and a red one for Ken--they looked ridiculous, two wigs fighting, so it was decreed that we should do it ourselves." Action came to a halt one day when, in a scene preserved in the final cut, Jacobi cannoned into a bookcase and all but knocked himself out. Another day was overcast by the fact that the ebullient young director insisted that his 53-year old co-star keep repeating a 10 foot dive: "We want to see the expression on your face all the way down, Derek!".

Sitting in his dressing room a the Theatre Royal, Haymarket, he stresses that the theatre was and remains his big love. Educated within spitting distance of Joan Littlewood's Stratford East stronghold, and regularly worshipping at the shrines of John Neville, Donald Wolfit, et al, he was "brought up surrounded by great theatre." And the theatrical gods smiled down on him. John Dexter spotted his National Youth Theatre debut, and kept an eye on him while he was acting at Cambridge. The gods did play one dirty trick. After three seasons at Birmingham Rep he was lured to Stratford upon Avon for what he thought were to be merely "talks", and found himself facing Peter Hall, Peter Brook, Michel Saint-Denis and John Barton--"it was like Olympus"--and instructed to read Ariel. Don't ring us, we'll ring you, they said when he had miserably finished, and when the phone did ring he was shattered to be turned down.

One door closes....Soon afterwards, Laurence Olivier happened to see on television a young unknown playing Marlow in 'She Stoops to Conquer'; very well indeed, and live. Inquiries were made, an invitation issued, and for the next eight years Jacobi worked his way through the classics at the newly-formed National Theatre. Thence to Toby Robertson's touring classical company; from there to the Royal Shakespeare Company, and on to Broadway.

In one particular respect Olivier remains his exemplar. Jacobi loathes the publicity machine. "I've never been at ease with it, and I never do chat shows--I'm not prepared to be fodder for them." Then he observes, after a pause, "I'm not my own greatest fan. This may sound paradoxical for an actor, but I really would rather not be noticed. That's what I admired about Laurence Olivier--the most famous actor in the world, and totally anonymous off stage. The sort of fame where you're constantly recognised, spied on all the time, must be soul-destroying.

His private life is carefully ordered, the world held at bay. He shares his Hampstead house with two cats and two hedgehogs; he gardens; he reads (but never his own reviews).

In the Edwardian opulence of the best dressing room in town, walking with the ghosts of his illustrious precursors, he radiates warmth and contentment. The table beneath the mirror is strewn with mementos, tiny birds, rabbits, bears, a pencil sharpener in the form of a skull. "Each one has an association with a time, a place, a play. I take them with me wherever I go." On the desk sits a teddy-bear, hurled on stage last week when he and Lindsay were taking their calls. "It landed between us. We didn't know who it was for, so we each held an arm. I have a lot of bears at home. People give me them. I don't know why."