Jeremy Irons, guest of honour at the Unicef luncheon, walks down the hotel corridor, his distinctive quick, jerky, clockwork stride not making much progress in the crowd. Dark brown hair, tragic eyes, brave smile - as twitchy as a thoroughbred and clearly naked without a cigarette. Although he reached 50 last August, he still looks like a vaguely sexually knowing public schoolboy from another time.

As always, there comes that slight surprise on finally seeing a very familiar famous face in person. There he is, tall and very thin, the accumulation of multiple personalities, still most memorably Charles Ryder in Brideshead Revisited; but there is also the hapless romantic from The French Lieutenant's Woman, or Father Gabriel in The Mission. That priest's relentless idealism has its appeal but it is difficult to forget the smooth and very strange Mittel-European aristocrat, Claus Von Bulow, accused of wife-murder in Reversal of Fortune, an Oscar-winning role in which Irons was cosmetically aged, bald pate and all, and barely resembled himself - except of course, for the voice, and even that was heavily accented.

Or there is his superb performance - or rather, performances - as the twin brother gynaecologists in Dead Ringers, David Cronenberg's terrifying psychological drama. And most recently, he was pathetic old Humbert Humbert, if played too sympathetically, in Adrian Lyne's uneasy version of Nabokov's Lolita. At a time when most film stars look like hired assassins, the gauntly attractive Irons could play a saint as easily, and convincingly, as he does obsessive lovers, wounded dreamers and sundry weirdoes.

Opinions vary: he is gorgeous; he's a wimp; he's a bit creepy, even sinister. He's very English, yet also exotic. In possession of the world monopoly on elegant melancholia, he appears born for costume drama, yet fits easily into present-day roles. His diversity is widely acknowledged and even his critics invariably concede, he is a good actor and a brave one at that, often taking risks - he never tries to be loved. And many of his characters are far from loveable.

While the above internal debate continues, however, he is suddenly gone. Photographer and reporter are faced with stalking the corridors looking for a hotel suite that is not where it should be. Better go back to reception. Suddenly a door we hadn't noticed swings open and Irons peers out, calmly remarking on the vastness of the room. So easy to get lost in.

On being presented with a Unicef souvenir necktie, he says thanks, but adds: "I never wear one." He is wearing bright red desert boots and seems very jolly, exuding an aura of "we're all in this mess together", and for a moment it's possible to imagine being in a war film, one of those 1950s British ones, with Irons playing the bright, inspirational, marginally demented leader intent that none of his men crack and we all get out alive.

He has been involved with Unicef for 12 years. "I'm an actor and I use that profile when it can help." No one could accuse him of trying to present himself as a hero. "I'm quite ruthless. Anytime I'm approached to do anything, I always ask `how much money are you expecting to raise?' Unless it is worthwhile - say £20,000 - I don't do it. I'm not a Unicef ambassador. I simply don't have the time. It is impossible to make commitments. I have a freelance involvement." Three years ago he visited Bosnia during the truce and saw the suffering at first hand. Although he says "sweetie" and "darling" his tone is brisk, almost businesslike; he lights a cigarette, rolls up his sleeves revealing thin, sinewy boy's arms, narrows his eyes with that short-sighted glance so familiar from his screen selves, and looks out the window leaving the observer to wonder what's going on in his mind.

Moments earlier as he sat being photographed, his attention seemed to be focused on the photographer's jacket, a hard-wearing piece of country clothing. As expected he comments, "I like your jacket", and suggests the name of the place in which the garment was purchased. It turns out he is wrong; it was bought elsewhere.

It doesn't matter, and Irons mentions how he has recently discovered how far superior working clothes are to fashion wear. His battered leather satchel has character, as does his aviator's watch. Irons, wearing well-worn corduroy pants, is clearly drawn to old, comfortable things and would probably be happy as a borderline eccentric. Though not born into vast wealth - "my father was a chartered accountant" - he has an aura of privilege, or at least of comfort. "I had a happy childhood, I was the third of three, it was wonderful." Born in 1948, he was raised in the Isle of Wight and says has never lost the feeling of being an islander off an island. "I'm sure it's made me very insular."

To a generation raised on growling, unshaven movie stars spitting out one-liners, the charm of the upper-middle-class English accent has given many British actors a natural advantage, fair or otherwise. Irons has a wonderful voice which has been used to fine effect many times, not least as the narrator of Granada's Brideshead Revisited, and of Lolita.

But as an actor he is extremely visual and acts with his face. "I'm interested in the balance between what one says and how one looks when saying it." In response to a comment made about the often bizarre emotional states many of his characters inhabit, Irons smiles his boy's smile: "I've always been interested in people who live outside my comprehension." Agreeing he is difficult to work with, he says matter-of-factly, "I'm a fairly blinkered person - I have corridor vision and when I'm working on something I tend to see nothing else."

Even at his most relaxed it is not too difficult to detect the determination which has directed his performances. "I have a forceful personality. If I say something, it is usually the same as what I think. People can find that difficult." Still, if he has personal devils, he keeps them to himself. There are no speeches, no accounts of having suffered for his art. His mobile phone rings for the first of several times.

On camera he often reveals a stilted grace, but his haunted eyes are eloquent. In Jerzy Skolimowski's Moonlighting (1982), Irons is Nowak, a Pole who arrives in London with a team of three Polish builders, to do a cheap and illegal building job for a man back in Warsaw. Nowak, a study in paranoia, has his orders and is in charge of the money. He is also the only one of the four who speaks English, but soon realises he is out of his depth. Desperate to succeed, he lies, cheats and shoplifts.

It is a small but urgent film set during the December 1981 military coup in Poland. Aside from urging the men to work at speed, he is preoccupied with keeping them ignorant of events back home. It is a fine performance redolent of fear, frustration and defiance. It consolidated the attention Irons had earned with his film debut, The French Lieutenant's Woman, a year earlier. Both films marked the real beginning for Irons, and made him the Ralph Fiennes of the early 1980s, although by then he had had extensive stage experience.

Even now, despite the number of movies he has made, it would be wrong not to mention Brideshead Revisited, one of the great achievements of British television drama. "That was 20 years ago," he says and he makes no attempt to conceal his pride in it. "It was very important; Granada seemed to be marking what was going to be the beginning of real quality television drama, something that was slow-moving and able to develop, unfold. But, sorry, no one has continued that type of series. Well, there was the Paul Scott (The Jewel in the Crown, based on The Raj Quartet) - but it seems all people really want on television is Ruth Rendell thrillers, all wrapped up in an hour. It is disappointing what has happened since." When Brideshead Revisited was revisited, or at least re-screened, last summer, TV reviewers attacked it.

Elegant nostalgia appears, for the moment, to be out of favour. "Well, that's because it was to do with the 1980s - but it was good," he says as a statement of fact. There is nothing defensive about his attitude. "We did the book, we allowed it to have its own pace." On a less idealistic level, Irons expresses his personal gratitude to the series; he has no problem saying it made him famous.

What made him an actor? He laughs out loud. There was no family tradition. "I think I was always in love with the idea of living outside the community", he says, and mentions having read various actor biographies: "Noel Coward, Charlie Chaplin, Garrick - there was the appeal of being beyond type, being on the outside". At 13, he went to Sherborne boarding school in Dorset. For a while he was "quite taken with the idea of being a vet; I was always interested in horses, but I had no aptitude for science - or for anything". How did he survive at school? Another laugh. "I got by; I played the system," which he manages to make sound rather exciting, and clearly did enough not to attract too much attention.

Acting for Irons is "pretty instinctive; I learn on my feet. I think the most important thing is not letting it look like acting. The secret is `don't act'. I have seen so many actors give good performances and everyone is impressed and you can see why, but at the same time, you find yourself saying `yes, but why is he acting?' " Unusually for someone involved in the film business, he seldom name-drops. At the mention of The Mission and the late Ray McAnally, he smiles with fondness and remarks, "he was a great man for stories, conversations were never short with him".

Again, unlike many actors, particularly those such as Irons, who have the face and voice to spend their careers with the Royal Shakespeare Company, he does not make the usual claims about theatre being his first love. When it is put to him that surely he should be a stage actor rather than a movie star, his response amounts to mild curiosity. "Theatre is very hard; you have to work long hours and be at your best at 8 o'clock at night, every night. It doesn't allow you to have a life around it." His phone rings again and he says with feeling, "it doesn't have to be Liscannor". Ah, builders.

Theatre was his education. On leaving Sherborne, he went to the Bristol Old Vic Theatre School and was a member of the Bristol Old Vic company from 1968 until 1971. Then he went to London to wait, in time-honoured fashion, for the big break. This came and he played John the Baptist in Godspell for two years. By then he had decided he liked the life and continued in theatre - "I just liked it. I could have been a stage manager, and was for a while" - spending the 1976 and 1977 seasons with the RSC. Ten years later he would return for more Shakespeare, appearing in A Winters Tale and Richard II.

Stoppard and Pinter would seem to be fairly natural territory for him as well, and he won a Tony Award on Broadway in Stoppard's The Real Thing in 1984. It is a part he loves and he admits: "I thought it had been written for me when I read it, but it wasn't. I think it was the first play Tom put his heart into. His work is always so cerebral." He has always admired Pinter - "I love the layered quality of his work; it's like setting out on a journey" - and appeared in The Caretaker at the Young Vic in 1974. Four year later, he was directed by Pinter in Simon Gray's Rear Column at the Globe.

He is an easy talker but acting is not his favourite subject; he is more ready with an opinion on a book or a movie he saw. At present he is reading Sebastian Faulkes's Birdsong. "I don't read as much as I should, but there are always scripts to read." People interest him. He says he is drawn to the baggage we all carry. "I like to know how people get to where they are in life. That's the glorious thing about falling in love - finding out each other's story." Possibly because he seems so obviously a type - the melancholy, depressed, romantic anti-hero - he feels compelled to take risks. "It is a fact that a script is written and someone says `oh yes, that's Jeremy Irons' and it will be because I have already done it." Comedy interests him. "I've done it on stage, and I'm good at it."

The remark doesn't surprise; he does appear to have a sense of humour. Relentless intensity is his medium but irony often underpins his performances. Irons's languid Aramis in Randall Wallace's recent offbeat remake of The Man in the Iron Mask was played with hilariously subtle, and saving, tongue in cheek. Would he like to direct? "If the right project came along. But it's easy to direct; it's bloody hard to do it well."

Anyhow, Irons currently has a project: the restoration of a 15th-century tower house a few miles from his home in Cork. Aside from a couple of personal calls - one from one of his two sons - the interruptions are from his builders. Irons is enjoying conversing in what is for him a new language, that of building. The availability of specific stone and timber is debated. He seems to be in charge. He has lived in Cork for several years and is breeding from a half-Irish draught mare. Even if he does look tired and haggard, he is buoyant, not cynical. His life seems easy. "It is. I'm very lucky." He married the Irish actress Sinead Cusack in 1978 ("we've been together for what? - 25 years"). They have two grown sons. More calls from the builders. He is in love with the romance of the 100-foot tower project as well as the technicalities. Is he restoring or rebuilding? Irons looks perplexed. "Is there a difference?"

Irons has made good films, but there have also been disasters. He refers to films he has been in with an impersonal detachment. At the mention of Damage, a sometimes-you-win, sometimes-you-lose expression passes across his face. "It was disappointing - wrong casting, and I think there was a lot do with the way Louis Malle was at that time." And then there's Lyne's Lolita which outraged so many in the US, it failed to find a distributor. It was released uncut in Britain. "It was risky and difficult." His performance is too sympathetic, and risks making Humbert a victim of love, however perverse that love is. Yet Irons's achievement is the extent to which he explores Humbert's obsession and, as Nabokov intended, his ambivalent guilt. Does he admire Nabokov's masterpiece? "It's very good," he says, seeming undecided. "It is overlong but there is some fantastic writing. And as a study of obsession . . . " his silence denotes approval.

Again he returns to extreme emotion as a powerful theme. Referring to Swann in Love (1983), he speaks about the difficulty of acting through another language. "I found it very hard. It is flawed. But I think it is an interesting film", and he mentions a woman who had brought her husband to see it, not for itself, but as an exploration of jealousy. "It is worth seeing for the emotion."

Cinema has first claim over theatre. He seems up to date with what is being released and knows what he likes. "I think it's good that people are going to the cinema," he says. For him there is no problem about working in the US. "There is no difference. There are so many Europeans working in film in the States." Claiming to live at a remove from the movie world, he does concede that he makes flying visits into it and agrees he always surfaces at Oscar time. "Well, it's always such a good time to see everybody." It is a life he can freely walk in and out of. "Of course there are days when I feel out of things and neglected and ignored and forgotten and no one loves me," but he's not complaining.