The IRA women ordered the teenager to go into the room to face the man she'd said had repeatedly raped her. "They said they would read the body language between us to determine who was telling the truth," says ****** Cahill, who doesn't want to reveal her first name.

"I was only 18. M, the man who raped me, was nearly 40 and a prominent west Belfast IRA member. The IRA women drove me to the flat in Kenard Avenue in Andersonstown. And then Seamie Finucane, the Belfast Brigade adjutant, walked in with M. I felt physically sick when I saw M.

"Seamie sat down on the living room floor, took off his trainers and joked about having smelly feet. It was surreal. This was meant to be a serious investigation into sexual abuse.

"M was handed the statement outlining the allegations I'd made. He said I was lying. 'You're a sick bastard claiming I did this to you,' he shouted. I yelled back that I was telling the truth. Seamie Finucane asked me to withdraw my statement but I wouldn't. I said I wasn't leaving the house until M admitted what he'd done. The IRA ended the meeting."

It's 10 years since that night in Andersonstown and Cahill sits in her own flat in west Belfast. She's an attractive, intelligent and confident young woman who now holds a good job in the criminal justice system.

Yet it takes her five hours, interspersed with countless tea breaks, because she becomes so emotional, to tell the story of how M raped her dozens of time when she was 16 and how the Provisional IRA and Sinn Féin engaged in a massive cover-up.

Speaking out isn't easy, she says, because loyalty to the movement is ingrained in her.

In republican terms, her family is royalty. She's a grand-niece of Joe Cahill, a Provisional IRA founder and former chief-of-staff who died six years ago. His photograph has pride of place in her house. She produces the copy of his biography that he gave her. "To cheeky face, my favourite niece, love Uncle Joe," he wrote inside.

She was Ógra Sinn Féin national secretary when the abuse began in the summer of 1997. She was working for the west Belfast festival radio station. M, an ex-IRA prisoner and leading member of the Provisionals' punishment squad in the Upper Springfield, was one of many republicans in the station.

Somewhere to stay

Danny Morrison, Jake Jackson, and Eoin O'Broin were all involved in the festival radio station. Caitriona Ruane was the festival director and Gerry Adams sat on its management committee. "My parents were on holiday in Donegal so I needed somewhere to stay that summer. M suggested I stay in Ballymurphy with him and his wife who was a relative," Cahill says.

"He told my parents he'd look after me. He talked politics with me and I was delighted not to be treated like a child. One night in the house, he was drinking tins of Harp and he offered me one. 'You're a big girl not a child,' he said.

"I hadn't drunk before that but I took a few tins. His wife went to bed. I fell asleep on the sofa. I woke up to find he'd unzipped my black trousers and pulled them and my knickers down. His fingers were inside me. I should have screamed but I didn't.

"I kept thinking his wife was upstairs and of the embarrassment this would cause in our family. I pretended to still be asleep. I was a virgin so what he was doing hurt me. He masturbated over me and rubbed it on my stomach. When I went to the bathroom later, I was bleeding."

M raped Cahill dozens of times after that. It always began when she was sleeping. "Every time, I pretended to continue sleeping. I know that was the wrong thing to do. But I was frightened because of his position in the IRA and I didn't want to cause pain to my family. When I didn't speak out the first time, it set a pattern which I now deeply regret – but I was only 16 then."

Worried

Cahill started rapidly losing weight: "I looked like something out of the famine." She confided in her cousin Siobhan O'Hanlon, Gerry Adams' secretary: "I told Siobhan that M was raping me and I was worried I could be pregnant."

She wasn't pregnant, and the rape stopped when she returned to live with her parents.

In 1998, Cahill told a north Belfast IRA woman. Later, she told a female Sinn Féin Belfast politician whose name is known to the Sunday Tribune.

That woman officially informed the IRA. In September 1999, a west Belfast IRA woman – whose name is known to the Sunday Tribune – instructed Cahill to attend a meeting that night. "I was told to stand outside Xtravision on the Andersonstown Road. A car pulled up and I was driven to the flat in Kenard Avenue.

"Seamie Finucane walked in. I was terrified. The IRA woman said: 'We're here because you've made allegations about M. We can't have these allegations circulating about a volunteer so we're investigating them.'"

Five months into the IRA 'investigation' Cahill was brought into the Andersonstown flat to face M. Several weeks later, the IRA brought Cahill and a male relative to a meeting. They said they'd closed their investigation and it was up to her family to deal with the case. It was the first time any family member had heard she'd been raped. "I burst into tears and my relative hugged me."

In July 2000, five months after the IRA had closed its 'investigation', two of Cahill's cousins – then aged 17 and 14 – came forward and said M had sexually abused them two years earlier. People had seen M lifting one of the girls drunk from a social club into a taxi. Neighbours had then watched him carry her from a taxi into his home. The IRA reopened the investigation. "I told them I wanted nothing to do with it," Cahill says. "I wanted to go to the Rape Crisis Centre. I said I needed professional help."

The IRA said M was under 'house arrest' in Ardoyne. Days later, Cahill was told he had 'escaped'. Now she confided in her Uncle Joe (80) whom she had wanted to protect from hearing she'd been raped. "He said, 'If I'd known I'd have told you to go to the RUC. There has been a f**k up of the highest order in the movement.'"

The word in Belfast was that the IRA had spirited M away to Donegal. "I don't believe he escaped," Cahill says. "The IRA facilitated him leaving. I never wanted M killed. I wanted him tied to railings in Ballymurphy with a placard around his neck saying he was a rapist."

She then had many heated meetings with the IRA and with Sinn Féin president, Gerry Adams. One IRA meeting at a flat in Andersonstown's Glassmullan Gardens was attended by Padraig Wilson, the IRA's go-between with the international decommissioning commission.

"He apologised on behalf of the army council that M had 'escaped'. I told him I wanted M brought back to Belfast. Padraig said the IRA didn't have the resources for that. I said it was only a two-hour drive from Belfast to Donegal, and the IRA had people in Donegal anyway that could go to the bed-and-breakfast M was staying in and fetch him.

"Padraig said: 'Do you think we should be running around after you?' I started crying. I said it wasn't just about me. M shouldn't have been allowed to go somewhere else he'd have access to kids."

Getting nowhere

After equally non-constructive meetings with Gerry Adams, Cahill stopped them, feeling "it was pointless, I was getting nowhere". She'd continued in Sinn Féin, addressing the 1999 anti-internment rally in Belfast and working for the party at Stormont. She remained a member until 2001 but grew increasingly disillusioned about how she'd been treated.

Even so, she wrote an article for An Phoblacht about her uncle Joe after he died. Inside, she was falling to pieces. She was on anti-depressants and sleeping tablets for nine years after she was raped. In 2006, she was admitted to the Royal Victoria Hospital after trying to kill herself.

Gerry Adams asked to meet her on release. "The first thing he said was, 'Are you still writing?' I lost my temper at his casual tone. I told him I'd been treated disgracefully and never once had the republican movement told me to go to the police or social services. I asked him to guarantee that no one abused would ever again be treated that way."

Later that year, M was spotted in the bar of Letterkenny's Clanree hotel. One of the two other children he abused had seen him in Letterkenny. Infuriated, their mother visited Gerry Adams. Cahill says: "She told me that Gerry replied, 'What do you want me to do, bar him from every bar in Ireland?'"

Cahill remains a republican but regrets that "a few powerful individuals put the preservation of the movement and their own position above the safety of children".