In a book to be published next month, the spy, who uses the pseudonym Kevin Fulton, describes in detail how British intelligence co-operated with the FBI to ensure his trip to New York in the 1990s went ahead without incident so that his cover would not be blown.

He claims the technology he obtained has been used in Northern Ireland and copied by terrorists in Iraq in roadside bombs that have killed British troops.

In the book, Unsung Hero, Fulton tells of his double life in which he had to play a convincing IRA man while working for the British. “You cannot pretend to be a terrorist,” said Fulton, who now lives outside Northern Ireland. “I had to be able to do the exact same thing as the IRA man next to me. Otherwise I wouldn’t be there.”

His allegations that the security services helped to obtain weapons that killed their own members follow revelations about British infiltration of terrorist groups and collusion in paramilitary killings.

The issue has been the subject of investigations by Lord Stevens, the former Metropolitan police commissioner.

Fulton’s book will include claims from his own experience that MI5 and the Special Branch of the Royal Ulster Constabulary colluded in the murder of their own officers and soldiers and allowed agents to be killed.

Fulton, a married Catholic now in his forties, was serving in the army when he was recruited by military intelligence to infiltrate the IRA. He later worked for the Force Research Unit, a covert branch of the Intelligence Corps set up to infiltrate paramilitary groups.

For 13 years Fulton was an IRA terrorist, involved first in courier runs, later as a driver and enforcer, and finally as a master bomb-maker in a unit in Newry, Co Down, credited with numerous advances in explosive technologies. “I was recruited as a serving British soldier,” he said. “I was in the Royal Irish Rangers. I agreed to go into the IRA as a soldier.”

Security sources have said Fulton was implicated in numerous bombings and shootings, allegations on which he declines to comment. He has said his handlers knew the nature of his role but ignored his warnings of forthcoming bomb attacks, including the Omagh atrocity, which killed 29 people in 1998.

Fulton and four other members of his unit in Newry pioneered the use of flash guns to detonate bombs. This technology was used in a bomb that killed Colleen McMurray, an RUC officer, in 1992. Her colleague Paul Slaine lost both his legs in the attack. He was later awarded the George Cross for his bravery.

Fulton claims he tipped off his handlers about this attack but they allowed it to go ahead to protect agents. “Two days before the attack on Slaine and McMurray I knew my officer commanding was using what we called a doodlebug, a horizontal mortar,” he said.

“I told my MI5 handlers and they took me to London for two days. The day I came back the bomb went off. The police were taken off the streets to allow the bomber to get in, set the device and get out.”

The trip to America came after the killing of McMurray, when the IRA had built sufficient trust in Fulton for commanders to send him abroad to buy remote control infrared devices that would allow IRA teams to refine the flash technique and detonate explosives from up to a mile away.

When he told his MI5 handlers about the mission, they arranged with the FBI to procure the detonators for Fulton.

In this month’s edition of Atlantic Monthly, Fulton outlines how an MI5 agent was sent ahead of him by Concorde to make preparations. He has also described the trip in interviews with The Sunday Times over the past few months.

In New York he attended a meeting with FBI agents and British intelligence officers. There he agreed to expose IRA operatives in America to the FBI. However, the same terrorists, who were arrested months later, were first allowed to procure and send the infrared technology to the IRA. Fulton claims this technology was used in the Troubles and forms the basis for insurgent bombs in Iraq.

A spokesman for the security service declined to comment.