His latest book, Stone Cold (Hutchinson pounds 16.99) looks set to generate more than the usual level of hysteria. It examines the rise, rise and eventual fall of the Irish loyalist killer Michael Stone, and includes the first detailed investigation into loyalist paramilitaries. Indeed its contents are rumoured to have forced the recent government ban of the Ulster Defence Association.
Dillon's books are toughly controlled catalogues of violence, but they offer insights into the minds and motivations of men involved in terrorism which go beyond straightforward reporting. The combination has earnt him impressive accolades. 'He's been very important,' says Conor Cruise O'Brien. 'Nobody else has done what he has done. It requires great personal courage and I think he's been living on his nerves for some time now'.
Until now, Dillon has kept his own life very much out of the limelight. He and his family moved to England from Belfast a year ago, after the threats from paramilitaries had finally become too persistent to ignore, and he still prefers to keep his exact address unknown. The inoffensive village where he now lives could hardly be further removed from the violence in his books, just as Dillon is actually nothing like the rather thuggish character who glares out from the photo on his dust-jackets. He has considerable charm; it becomes obvious how he managed to gain the confidence of everyone from the IRA to the RUC. And listening to a string of wicked anecdotes in his kitchen, it is easy to forget the danger he's been living with for the last 20 years.
Dillon is hardly a shy man, but he exhibits a magnificent disregard for situations which would have most journalists gibbering under a table. He was once hooded by paramilitaries before an interview and made to lie down in the back of a car. He was in the middle of investigating a series of murders that began with exactly that tactic, but he says only that it was 'quite scary'. This could seem like mere bravado, except that Dillon has made a habit, ever since he worked for the Belfast Telegraph during the early 1970s, of taking on situations that few other people would touch. His experiences inspired what he agrees is more or less a personal crusade. 'It was then that I began to realise the true nature of violence. And I wanted to challenge the tacit acceptance of it.'
Soon afterwards, he co-wrote his first book, Political Murders in Northern Ireland (1973), still seen as the authoritative work on the subject. For Dillon, then in his early twenties, this was a tough time. Older, wiser and more stoical now, he still hesitates when describing his experiences. 'There was a body in an alleyway in Belfast. It was a young man . . . he had been branded and burnt with a poker. I remember ringing my paper and saying, this person has been tortured and here's the extent of the torture. It was the first time that sort of thing was admitted; perhaps the RUC were determined not to inflame passions. But I thought it was in the public interest for people to know.'
It's the old cry of the journalist, but Dillon is reluctant to count himself as one. He has been a BBC radio and TV producer, playwright and Channel 4 News analyst, but he describes himself simply as a writer. His books have been compared to non-fiction Le Carre, and he admits to a stylistic complicity with such parallels. 'I wrote in a kind of fictional style, not a journalistic one. I wanted to make it easier for people to read - I think a lot of non-fiction is very dry, very stilted and I wanted to give a sense of what violence is about, to let people know what's going on.'
Other journalists have leapt on this with glee, accusing Dillon, particularly in his last book, Killer In Clowntown (1991), of everything from egotism to unprofessionalism. Dillon himself is philosophical. 'They're my worst critics. All journalists think there's a book in them somewhere but never really get round to writing it.' He can understand that, too: there was a gap of 16 years between writing Political Murders and The Shankill Butchers.
'I was trying to get away from conflict,' he recalls. 'I joined the BBC as an arts producer and felt free, free from covering it.' But he was irresistibly drawn back; arts programming became current affairs, which then became an investigation into one of the most horrifying series of murders in Northern Ireland: the story of the Shankill Butchers.
Dillon is entirely matter-of-fact about his choice of subject. 'People always say, why write about conflicts, but it's the centre of human life. Before people were writing about it they were painting it on cave walls. I suppose as a writer you've got a mission to explain the things around you. And what surrounded me was death and destruction.'
The move to England has done more than change the setting. He admits that he is now more free to express himself. But he's also finally found the freedom to move on - the publication of Stone Cold will, he claims, mark the end of his work on Ireland. He is now writing a novel - the subject is under wraps - called The Year of Dreams. Dillon has described the 'year of dreams' elsewhere: it was 1968, when protest movements around the world generated a mood of dynamic optimism.
Dillon and his family are now equally optimistic. But in Ireland that mood was swept away by a tide of violence, resulting in a legacy which Dillon admits is unavoidable. 'I don't think anyone who leaves the place can escape it. I don't think even Beckett did.' And there is still a residual sense of loss, the bittersweet taste of exile. For a writer who 'just wanted to explain', Dillon, now contemplating a move to France, has perhaps been as much a victim of the Troubles as the people he writes about. He shrugs, not denying it, but deflecting any sympathy elsewhere. 'We all have. That's the real thing to understand'.