Leader: This is the best deal the Unionists can hope for

WE DO not need to accept the Prime Minister's melodramatic suggestion that this is Northern Ireland's one and only chance of lasting peace to recognise that we have indeed come to an extraordinary moment. As Tony Blair pointed out yesterday, the republicans have moved. The Unionists scorned the description of Sinn Fein's offer as "seismic", but it is hard to avoid the - metaphorical - conclusion that the tectonic plates of Irish politics have shifted.

Gerry Adams has, very specifically, made his serving in the government of Northern Ireland conditional on IRA disarmament. That was promised in general terms in the Good Friday agreement last year: now Sinn Fein has tied itself to specifics. If the IRA does not start disarmament within weeks of Mr Adams and Martin McGuinness taking office, and if the IRA does not complete its disarmament by May next year, then Mr Adams and Mr McGuinness will be out again. And the question of whether the IRA has fulfilled its obligations is to be decided by an independent third party, the Canadian general John de Chastelain.

That comes as a shock to those, from both traditions or neither, who thought that the IRA would never disarm, or who doubted that Sinn Fein could genuinely speak for its military wing. It is such a shock that many Unionists have not realised that their objections to doing a deal with Sinn Fein simply do not apply. As Mr Blair rather brutally pointed out yesterday, the Good Friday agreement did not require disarmament as a precondition of Sinn Fein joining the executive of the Northern Ireland Assembly. It was the other way round - if Sinn Fein joined, decommissioning of IRA weapons had to follow. That was the sticking point for David Trimble during the Good Friday negotiations. He was able to hold off the doubters in his party with a handwritten letter from the Prime Minister confirming that, "the process of decommissioning should begin straight away". That did not happen, and to that extent the unionists are justified in their suspicion of Mr Blair.

Since then, Mr Trimble has been trying to find a way of making the start of disarmament and Sinn Fein's entry into government happen at the same time. But the Unionists should realise that what they have on the table now is better than that. It contains the legal guarantees - which they could not obtain in the Good Friday talks - that if disarmament does not happen, Sinn Fein will be kicked out. And it provides for the IRA to disarm entirely within 10 months.

As Mr Blair said yesterday, to "refuse to put the issue to the test" would allow Sinn Fein a "massive propaganda victory". It would be to betray the silent majority in Northern Ireland who voted for the Good Friday agreement in last year's referendum. And it would be to betray the thousands of ordinary unionist families who want, more than anything, the normalisation of life in their part of the United Kingdom. The Unionists must say Yes.