Jack Straw's intervention in the release of four of the IRA's most vicious terrorists - including Brighton bomber Patrick Magee - has come at a turning point in the Northern Ireland peace process.

Downing Street has insisted the move is not politically motivated as a way of putting pressure on the IRA to start decommissioning arms - the issue which threatens to run the process into the sand.

But there was no doubt that the sight of three of the prisoners walking free on Tuesday would have piled even further pressure onto the knife-edge negotiations.

Two of the prisoners were serving life sentences for the Chelsea barracks bomb and a third was involved in the plans to bomb English seaside resorts.

Under the Good Friday peace deal, the three could have walked free on Tuesday.

Magee, who came close to wiping out Margaret Thatcher's Cabinet with the bomb attack on the Grand Hotel in Brighton during the 1984 Tory party conference, would have been released in June.

The home secretary has insisted that the move to stall the releases pending a possible review has been prompted purely by legal technicalities.

Controversial move

The men were convicted by English courts, not in Northern Ireland.

Mr Straw is seeking clarification of whether the length of time they have already served has been calculated correctly.

The move is certain to spark anger and claims that it is an attempt to influence the peace talks.

But ministers could have done without the controversy at such a sensitive time when it could easily throw the talks off track.

Hard-line unionists, led by Ian Paisley junior swiftly attacked the move, claiming there was one law for people who committed terrorist crimes in Britain and a different one for those who committed them in Ireland.

And there are fears that the republican movement will also react badly, suspecting the government is trying to force the issue of arms decommissioning.

It had been believed that the prime minister was ready to personally intervene in the stalled peace process in a bid to forge a final breakthrough over the arms issue.

But it now seems likely the talks may be taken right up to the new 2 April deadline with the real fear that they could collapse.