The film is Welcome to Sarajevo, loosely based on the story of Michael Nicholson, the ITN reporter who was so struck by what he saw in Bosnia that he smuggled a child out to live with him and his family in Britain. In a gripping, agonising tale, Dillane makes a superb focal point, as handsome as the movies demand, as smoothly charismatic as telly stars tend to be, but also intelligent, subtle and convincing ("He's got me perfectly," Nicholson has said). Dillane shines in a strong cast (Kerry Fox, Juliet Aubrey), and you come out feeling that given the right roles, he will soon be up there with Ralph Fiennes and Daniel Day-Lewis. He too has reached the multiplexes via the stage - like the others, he has played Hamlet in London. Yet his performance in Welcome to Sarajevo is the opposite of stagey.
When I put this to him, there's a pause.
"Yeeeess." But then he agrees. "I was just looking at my diary." He picks up a stocky notebook, bulging with foreign-page cuttings. "One of the first things I wrote was, How to find a style? I'll read it to you. Impulses: to not 'act'. The act of acting seems vain, artificial, in this context. Is there some style which could serve the film's purpose without drawing attention to itself? So it all came out of the fact that actually" - he sniggers - "I didn't want to do the job at all."
Really? "I was very wary of it. The war had just finished, or at least a treaty was signed, of some sort. And here was Hollywood coming in and saying 'we're gonna make a movie', about this English journalist who saves a young girl from the orphanage under fire and brings her back to England. And to me that's a dangerously mawkish and sentimental story. Or could be."
He changed his tune after meeting the director, Michael Winterbottom, a graduate of Cracker, and seeing his previous work. Winterbottom's most recent film, Jude (1996), had its faults, but could hardly be accused of mawkishness. "The thing about Michael is he avoids those Hollywood moments - those traditional escape-routes for the audience's emotions. It's to do with getting out of the way of the emotional drag of the story, which is beyond the individuals concerned."
Winterbottom makes the same point. "Stephen was initially suspicious of the whole project, and that discomfort carried into the acting. He was very concerned not to make the film about his own character."
This is the paradox at the heart of Welcome to Sarajevo. It's the story of an individual, with whom the audience must identify. But its real purpose is to educate us about a war - a particularly vicious one, which took place under our noses, and yet we barely noticed the smell. The setting, Sarajevo itself, is more central than the central character.
There is also what might be called the Schindler's List problem. The subject is man's inhumanity to man, yet the hub of the narrative is a good deed, or an attempt at one; and the protagonist is an outsider. "By saving a child, he saves himself," Michael Winterbottom says. "Stephen was very nervous of that. He wanted to make sure that it didn't dominate the film."
Dillane is lunching on dried apricots, spurning the cheeses that the PR firm has also laid on. He is slight, and what weight he has is not thrown around. But on the screen, he is especially good at capturing the self-regard of the TV reporter. The real Michael Nicholson does exude a certain arrogance as he brings us the world's troubles.
Dillane says nothing, but smiles broadly. "Well, they're stars, aren't they."
To research the role, he hung around ITN and also spent time with print correspondents. He came out of it with more respect for them. "I responded to their dynamism. They really did want to get this stuff out. Though there's a whole other side to it, which they don't deny - there's a lot of adrenaline in a war zone, a lot of kicks, life is simple and the normal rules don't apply. But they are risking their lives. There's something quite noble in that."
In one of the film's telling moments, the news that there are concentration camps in Bosnia is placed second by the editors back home to the Duke and Duchess of York's break-up. Dillane feels that the war reporters were left asking hard questions of themselves. "There was huge self- doubt among them, which has manifested itself in Martin Bell's virtual retirement. How do you tell this stuff? How do you do it? I personally don't believe objectivity is possible; I don't think this apparent BBC objectivity is of any value. It hinders the truth, because things become a series of disparate facts, devoid of meaning."
This is where the film triumphs. It makes you feel that finally, you know what was going on. "I read the papers," Dillane says. "But my feelings about the conflict were as confused as anyone else's. At times it seemed so clear what was going on, how could we not be doing anything? And then the fact that nothing happened made you think that perhaps there's some other story, that Douglas Hurd knows and the rest of us don't. You feel as if you can't commit yourself. It's the whole question of whether you've ever got enough information ... Maybe things have changed with this new government. We were living in an extraordinarily cynical age then ... " His voice, mellow and persuasive, trails off, as if he hasn't persuaded himself.
His acting career has had two phases, first mainly television, then mainly theatre. This year he was acclaimed, in this and other papers, for his performance as Clov in Beckett's Endgame at the Donmar Warehouse. Before that he was Peter Hall's most recent Hamlet, at the Old Vic. "I see Sarajevo as a natural progression from those two. They're all the same stuff, really. 'The impossibility of death in the mind of the living', isn't that how Damien Hirst put it?"
On television, he is best remembered for Lindsay Duncan's gorgeous, pouting bit on the side in The Rector's Wife. His hair, long for that role, was as clipped as a war report for Sarajevo. Now it's heading back towards windswept.
And the third phase may be starting. He stars in another forthcoming film, Firelight, a period love story with Sophie Marceau. "I haven't seen it, so I'm not sure what it is. I sense it's Jane Eyre-ish."
None of this would have happened without Trevor Eve. Dillane, the English son of an Australian surgeon, read history and politics at Exeter University. "Went into college directionless, came out of college directionless, travelled for a bit, thought I'd better get a job." So he trained as a reporter on the Croydon Advertiser. "We each had to read a national paper, trawling for local stories. Mine was the Daily Mail, for my sins, and one day there was an interview with Trevor Eve, a small piece about how he got into acting. I think he'd trained as an architect and got pissed off with it. So I thought I'd do that." He went to the Old Vic Theatre School in Bristol. He still hasn't met Eve.
Dillane has an aura of stillness, far from the neuroses that afflict both actors and journalists. He and his long-time partner have a six-year- old son and a baby due in May. "I don't think he's particularly dreaming of golden days by the pool in LA," Michael Winterbottom says. "He's certainly got the attributes - good-looking, intense, bright. But he's doing a film in Ireland, and then a play, so he hasn't rushed into the first American film he's offered - " He interrupts himself. "That stuff about being good-looking would make him cringe."
'Welcome to Sarajevo' (15) opens nationwide from Fri.