"THE old man's name was Guiseppe Conlon, a man that meant little to me then but was to haunt me for the rest of my life. I had been asked to visit this man but nothing could have prepared me for the sight of him as he came in - an emaciated, old man, gasping for air. `I am an innocent man' he said to me. I was very worried, I had never seen a prisoner so ill. He was almost crushed and broken. With every breath he said, `I am an innocent man, and then he would say he had faith in British justice, as I myself did at the time."

In January 1970, on a commuter train between Reading and London, a man she had never met before began talking to Sister Sarah Clarke. He told her about a civil rights march he had taken part in a few weeks earlier. Perhaps because he had recognised the nun's habit or perhaps because "being an Irish nun, he thought I might be sympathetic", the man felt confident enough to describe the events of the four day march from Belfast to Derry, which became known as the Burntollet march. As soon as possible, Sister Clarke went to her Mother Superior and asked if she could join the civil rights movement. As she says, "It made a big impression on me. I felt I needed to do more than just pray for peace."

Speaking to Sister Clarke, now aged 76, some 26 years later, one is struck by the incredible sureness of her voice. And also that it has taken a long, long time to persuade her to tell the story of her work, as she does in her new book, No Faith In The System.

That first encounter on the train prompted Sister Clarke to join the now defunct Northern Ireland Civil Rights Movement (NICRA), becoming its secretary within a few weeks. Sister Clarke relates how, when NICRA organised a march on the first Sunday of July each year, they would warn their members to "sew up their pockets in case something was planted on them. Even the coppers in their pockets were considered offensive weapons. Despite my years, I was very, very naive."

Sister Clarke's relationship with NICRA, which had become tainted with internal divisions, came to an end in 1972. In her book, she says that in these years, when she was working primarily for the repatriation of prisoners, she questioned herself for the first of many times. She asked herself whether critics among the clergy and in the prison service were right in saying she should be carrying out her religious work elsewhere. "I sometimes used to feel that I was in the wrong place. I knew it was the right thing to do, but at times, felt perhaps it was too political."

Those critics may have caused her many times to question her methodology - but never, thankfully, she says, her convictions.

Sister Clarke's life as a young nun in Ireland was, she says, a form of preparation for her life's work with prisoners - the lack of privacy, the reading of private letters. But the big difference was that "we choose it and we are free to give it up any time we like".

In the foreword to No Faith In The System, Albert Reynolds describes Sister Clarke as "the moral good Samaritan, working at the coalface...".

Sister Clarke says it was "the families who were brave and continued to suffer - but they were innocent".

She admits in her book that the prisoners are "alright, they are inside" - life is tough, but the families left without fathers and husbands carry a heavy burden.

During the 1970s, when Sister Clarke's work with the families of prisoners was at its peak, she estimated the cost to a prisoner's family of travelling from Ireland to, say, Whitemoor prison, or the Isle of Wight. It was £600 for each trip and the majority could barely afford it. The families found themselves locked into an endless round of pinching and scraping "pulling back and denying themselves little comforts", to pay for the trip.

Eventually, the authorities from Sister Clarke's order called a halt to prisoners' families being accommodated at their convent; and Sister Clarke became a persona non grata with the British establishment, banned from visiting category A prisoners. This was when many long term friendships were formed, when, instead, she queued with families outside Whitemoor and Brixton prisons to hand in parcels containing cigarettes, or an Irish newspaper, or even a shirt donated by a neighbour. The queues provided a great source of information.

"Imagine if you had travelled from Ireland and had your children with you. First you had to hand in your visiting order, then another queue to hand over your parcel and then get in the next queue to get in for your visit." The experience, she says, was "an education: I learned a lot about the lives of prisoners' families, their grievances and hardships, the injustices they suffered."

It was not always easy. "I sometimes thought `why can't I be nice and comfortable like the rest of the nuns, stay inside and mind my own business'," she says. But as soon as the thought would come to her the phone would ring and someone would say: "Sister Sarah, such a one is at the train station or at the airport.' I couldn't say no. I just couldn't say, `well, I am afraid to go'. I just had to keep on going.

"At times I would have worked if everything ended, because I loved teaching, and would go back to it. I was scared that if I said no, the poor family would land in Heathrow and wouldn't know where on earth to go, what to do, and they could have been arrested. So I just had to keep going."

Sister Clarke believes that if there is to be a peace process, Irish prisoners in British jails should be transferred to be near their families. "I don't know why politicians drag their feet.

I THINK if Christ were here today, the people He would condemn would be the politicians in government. He never condemned a sinner. Never, never, never. He might tell them to stop sinning. He called Herod a fox, and I think He would call a whole lot of politicians foxes. And they are really responsible. If they talk, there would be no violence, of that I am almost certain."