Denis Murray in Belfast: "The move comes at an incredibly delicate time in the peace process"

The four men include Patrick Magee who was given seven life sentences for his part in the 1984 Brighton bombing which nearly wiped out Margaret Thatcher's Cabinet.

The Home Office insisted the intervention was on a point of law and had nothing to do with the Northern Ireland peace process which is going through an increasingly tense period as the deadline for the devolution of power to the province, 2 April, approaches.

Sinn Fein have responded to the move with anger and have accused Mr Straw of "unacceptable interference" with the Good Friday Agreement.

Sentences reviewed

Three of the men, Thomas Quigley, Paul Kavanagh and Gerard McDonnell - had been due for release on Tuesday.

Patrick Magee: Given eight life sentences

They had all made successful appeals to the independent Sentences Review Commission which then brought forward their release dates.

The same body brought Magee's release date forward to 22 June.

Originally it had been expected that the prisoners would all have been released on 28 July 2000, the date by which all terrorist prisoners are due to be released under the agreement.

Denis Murray in Belfast: "It is likely to make republicans very angry indeed"

But Mr Straw has obtained an interim order setting aside the commission's rulings.

He will seek judicial review of the commission's decision on Tuesday at the High Court in Belfast.

The four men are said to be the first life prisoners convicted by the English courts to come up for release under the scheme which has so far seen the release of 250 terrorist prisoners since it began.

'Clarify the law'

With a number of similar cases in the pipeline, the Home Office said: "The government thinks that it is important to clarify the application of the law as it applies to prisoners transferred from England and Wales to Northern Ireland."

Gerry Kelly: "The move is political"

But Sinn Fein spokesman Gerry Kelly accused Mr Straw of interfering with the peace process and demanded the immediate reinstatement of their release dates.

He said: "This is unacceptable behaviour by the home secretary. Once again he is interfering in the Good Friday agreement," he said.

But the Conservatives back the move.

Shadow Northern Ireland secretary Andrew Mackay said: "We believe it is right that Magee and others convicted of terrorism on the mainland should not be included in the government's early release scheme," he said.