My friend Sean: a patriot who turned from terror to become an inspiration

And, as another summed up the essence of his life after he decided the IRA was evil: "He saw his life as one of expiation and to that end, never lost the opportunity to confront the ancient Irish Spirit that has caused so many young and good Irishmen to rush 'Gaderene-like' to murder and mayhem".

Sean was brought up in a Kerry family of true believers. By the time he was 20, he was an experienced terrorist who had murdered two people in the name of a united Ireland. Eva Martin and Peter Flanagan would haunt him for the rest of his life. He left the IRA at 20, but returned to atone as an unpaid spy for the Garda Siochana.

For the 22 years I knew him, Sean was an enemy of ideological enslavement. His life was under threat but - always fiercely independent - he refused to be bowed by that. The IRA were very clear about the repercussions of being an informer. As Martin McGuinness once helpfully explained on television, the penalty for changing sides was "Death. Certainly".

I met him in Maghaberry Prison in 1995, intrigued by some fascinating articles he had written about the republican movement. In a couple of hours, I learned more than I'd ever got from books and journalism. He was an exceptionally acute observer of people, which is what made him such an effective spy, who had risen to lead the IRA's Southern Command along with Martin Ferris, now a TD. He also had what a publisher friend of mine described the other day as a "meat-cleaver" mind.

From then on, we would talk frequently on the phone and I visited him often, usually accompanied. Perhaps the most memorable occasion for me was when I brought with me a part-time policeman who had worked for years in the part of Tyrone Sean had terrorised as a young man. What, he asked Sean delicately, was "your stamping ground?" I listened as they exchanged information on local IRA activists, their abilities and their crimes and their potential.

Ulster Protestants forgive those who repent, and he is one of innumerable one-time targets of Sean who became a friend and is deeply distressed today.

Sean was our Hibernian Kremlinologist. But he also had the priceless advantage of understanding loyalists and mainstream unionists. In jail, he had been put in a loyalist wing once he was outed as a spy and he nearly died when one of them poisoned his coffee. But gradually he won their trust by listening to them intently and treating them with respect.

By the time I met him, he had formed good relationships with a variety of prison guards and police. Some could never forgive his past, but far more developed a great liking and respect for someone who was facing the evil he had done in his youth by putting his life on the line to defeat the ideology he had come to recognise as pernicious.

In February 1996, at a conference on Northern Ireland, I was told by an appalled Northern Ireland Office senior civil servant that the IRA had just broken the "cessation" with a massive bomb in Canary Wharf. "That's 10 days earlier than Sean O'Callaghan predicted," I said. The vast majority of those present were absolutely incredulous at what had happened, and I thought not for the first time of the absurd irony that the British had in one of their prisons the best analytical mind on IRA terrorism, who was ignored by both them and the Irish government. An exception was the then Leader of the House of Lords, Lord Cranborne (later the Marquess of Salisbury), one of the few Conservative politicians who cared about Northern Ireland, whom I put in touch with Sean and who had him talk to about 12 members of the Cabinet after he had been released from jail. I overcame the scruples of David Trimble too, who found him an invaluable (unpaid) adviser on the negotiations.

He was neither nationalist nor unionist, but he cared deeply about the democratic rights of the people of the island. But he couldn't visit the country of which he was such a proud patriot, and was exiled from the Kerry he loved so deeply. To his dying day, he was a reader of local newspapers and could have told me, had I cared, how Kerry was doing in GAA sports. And his ashes will be scattered there.

As one of his intimates, I would provide Sean with a safe house from time to time at short notice, assumed my phone was bugged, and was constantly drawn into his ingenious anti-terrorist schemes. In his first years out of jail, he was erratic and had no sense of time. Since he had turned down the police offer of a change of identity and round-the-clock protection, they offered him nothing at all except a bullet-proof vest that ended up in my attic, but they did provide numerous intelligence warnings about imminent danger. What made me angry, though, was the way he was treated by the state he loved and for which he had worked unceasingly. He was seen by the Department of Foreign Affairs as an enemy of the peace process and while members of the IRA Army Council were welcome, Sean was a non-person.

It was often nerve-racking, and the strain on him was terrible. He had one minor breakdown and relied too much on cigarettes and alcohol. He would tackle the alcohol - and, typically, in the process make in AA another huge cohort of friends - and had been sober for almost five years when he died, but although he tried again and again to quit tobacco, he never succeeded. A terrific companion and tremendously well-informed about politics and much more - for he was formidably well-read and wise - people queued up to spend time with him, and he preferred reading or talking to establishing a career, partly, I came to realise, because he couldn't bear to be told what to do.

On leaving jail, he had turned down a lucrative offer from the Sunday Times to be a full-time correspondent because it would compromise his independence. But, living on half-nothing, he gave much of time to working with groups trying to tackle such social problems as knife crime and Islamist grooming.

Always, it related back to his horror at what he had done. "Just as some young Muslims are drawn to a purist and reactionary interpretation of Islam," he wrote in the biography he published last year on James Connolly, his one-time hero, "there are still young men and women today who are being duped by a purist and reactionary narrative of Ireland's humiliation at the hands of its ancient enemy. These are powerful forces for fanaticism, kept alive by songs and poems, stories and myths, nourished by some who should know better, and peddled by others who are true believers with hate-filled hearts."

A punchy writer, his memoir, The Informer, was a critical success and a bestseller, but he spent what he earned from it on family and entertaining his friends. He was a man with no interest in material possessions: he has left his children only books, an unfinished novel on the making of a "true believer", and a pride in their usually absent father who put his country before everyone and everything.

"Looking back from where I have come from," he wrote in his Connolly book, "and with my experiences of good and evil, I can see it requires above all else a firm and unflinching determination of promote the hard-won centuries-old values of liberal democracy. Some values systems are worthier than others and, as we face a complex and uncertain future, it is now more important than ever that we make the right choice."

Reviled by many in the island whose people he served all his life, badly and then well, he wrote a poem at a time when he had betrayed IRA comrades like Martin Ferris TD (who went to jail for 10 years) to stop an arms shipment:

Like so many others, I loved and will desperately miss this inspirational man. He was a great patriot who did his ungrateful state much service. I am proud I was his friend.

Over a pint of Guinness

In Quane's pub in the village

I got to thinking about the value

Of being an informer.

On our television screens

I know that friends and neighbours

See the ghost of Roger Casement

March on the Banna Strand.

I see seven tons of American

Guns and bullets

Towed into Queenstown, or Cobh

As we call it now.

My Guinness and my secrets satisfy.

Seventy-six thousand bullets

Will not shatter one limb,

Or spatter brain on a pub floor.

I finish my pint and walk

The forty yards home.

It's been a long, hard week.