The Joint Support Group (JSG), which runs agents under the control of the Intelligence Corps, is one of a number of units expected to leave Belfast as part of the “normalisation process” under which the Government plans to cut troop levels by more than half to about 5,000.

Paul Murphy, the Northern Ireland Secretary, announced in February that MI5 will take over primacy for national security intelligence in Northern Ireland by 2007.

The JSG is the successor of the Force Research Unit (FRU), which acquired notoriety in the 1980s amid allegations that the unit of about 40 intelligence officers colluded with Special Branch officers of the Royal Ulster Constabulary and the loyalist terrorist Ulster Defence Association (UDA) in the murder of several republicans.

Brian Nelson, who was the UDA’s chief intelligence officer when he was recruited to become one of the FRU’s top agents, was jailed for ten years in 1992 after admitting five counts of conspiracy to murder. He died of a brain haemorrhage in April 2003.

The FRU and its former leader, Brigadier Gordon Kerr, who became military attaché in Beijing, are the subject of continuing inquiries by Lord Stevens of Kirkwhelpington, who retired as Metropolitan Police Commissioner in January.

The JSG has continued the role performed by the FRU, although agent-handling rules were tightened after concerns were raised over the level of control of informers after Nelson’s confessions.

The Government’s intention is to complete the withdrawals from Ulster within two years of a final peace settlement but steps are being taken to exploit the unique experience gleaned in Northern Ireland in theatres of operation elsewhere in the world.

This month Geoff Hoon, the Defence Secretary, announced the establishment of a new regiment, the Special Reconnaissance Regiment (SRR), to provide covert surveillance expertise for operations by the SAS and the Special Boat Service.

Although he did not specify which experts he had in mind, the new regiment is largely based around the surveillance specialists of the 14th Intelligence Company, also known as “the Det” (Detachment), which has operated in Northern Ireland for many years.

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