MI5 is to take the lead role in Northern Ireland on issues of national security, Paul Murphy has announced.

In a written Commons statement, the Ulster secretary insisted the move would not undermine the Police Service of Northern Ireland (PSNI).

He said the review of the province's policing, conducted by Chris Patten, had always made it clear that national security would remain a matter for central government.

After a "lengthy period" of consideration, Murphy said he was convinced that the argument remained valid.

"The very serious threat from international terrorism which has developed over recent years has reinforced that conclusion," he said.

As a result MI5, also known as the Security Service, will take over the lead responsibility for national security intelligence in Northern Ireland, replicating the position it has held in the rest of the UK since 1992.

Sharing intelligence

Murphy said: "Such change will in no way diminish the role of the PSNI in intelligence gathering in areas other than national security, nor of course in mounting executive policing operations, making arrests and taking forward prosecutions."

"Looking to the future, such a change will facilitate the devolution of justice and policing when a robust and workable basis for that is agreed, taking account of the fact that national security is an excepted matter for which the secretary of state must remain responsible.

"In the meantime there are important benefits in bringing the arrangements for national security into line with the rest of the UK so as to provide for a consistent and coordinated response to international terrorism.

"Sharing of intelligence on a cross-border and international basis will be particularly important in combating money-laundering and other aspects of organised crime."

Murphy added that the PSNI and Security Service would "continue to work together in partnership", with the police force providing the operational response in countering terrorism.

"We intend that the new arrangements, together with associated safeguards, will be fully operational during 2007," added the secretary of state.

"This timetable reflects the need for detailed planning and implementation."