Explaining why responsibility for MI5 would continue to be controlled by the UK Government after the devolution of policing and justice powers, the Northern Ireland Secretary said the possibility of al Qaida targeting the region had to be considered.

While stressing there was no current intelligence suggesting an attack was imminent, Mr Woodward said Northern Ireland was vulnerable.

"It's inconceivable that the very threats that are experienced in Great Britain or indeed in the Republic of Ireland won't also be threats here in Northern Ireland," he told Assembly members.

"And to imagine that they couldn't be or wouldn't be, and to take no precautions on that basis, would be very foolish."

Mr Woodward said national security in the region was no longer just about tackling the threat from home-grown paramilitaries, and as such it had to be dealt with by the British Government in terms of the overall threat to the UK.

Outlining a new protocol that will define the links between Stormont and Whitehall on the issue, he insisted that the region's new justice minister would be informed by the Secretary of State about matters that related to Northern Ireland.

Acknowledging that some people in the region still viewed the security services with distrust as a result of operations during the Troubles, he told the Assembly and Executive Review committee that all national security decisions taken would be accountable.

He said: "In relation to the present and to the future let us be clear: the Secretary of State and Home Secretary are both responsible and accountable to parliament and this protocol contains a presumption for communication and the structure implied only points in that single direction."

Mr Woodward said an independent reviewer would be appointed to scrutinise national security decisions taken in Northern Ireland in a bid to instil confidence in the structures.