Leading Article: John Hume must help clear the way for a Unionist Yes

THE HEAT is on David Trimble to decide. If his Ulster Unionist Party says Yes on Thursday to the plan produced by Tony Blair and Bertie Ahern, the peace process in Northern Ireland will move to the next decisive phase.

But this week is also decision time for Mr Trimble's co-Nobel Laureate, John Hume, the leader of the most neglected party in these negotiations, the constitutional nationalist SDLP. Mr Hume can make a Unionist Yes possible if he is prepared publicly to underwrite the Blair-Ahern proposals. Mr Trimble set out his bottom line yesterday. He wants guarantees that Sinn Fein will be ejected from the devolved government of Northern Ireland if its military wing fails to disarm as set out in the Blair-Ahern document.

Mr Trimble's demands are eminently reasonable. He wants to be sure of two things. First, that if the IRA starts to prevaricate or quibble about disarming, Sinn Fein really will be kicked out of the Northern Ireland executive. The Unionists can all too easily see how the whole business of postponements and movable deadlines could continue to apply once Gerry Adams and Martin McGuinness get their feet under ministerial desks. There remains an alarming vagueness about Mr Blair's assurances that the IRA must make a statement "within days" of Sinn Fein taking office and start to hand over weapons "within weeks". General John de Chastelain's decommissioning body should set out a timetable with specific dates, and the draft legislation which Mr Blair is to produce this week should tie Sinn Fein's automatic disqualification to those dates.

Secondly, Mr Trimble is concerned that, if Sinn Fein is expelled from government, the remaining parties who have stuck to their undertakings should be allowed to continue in power in a devolved administration. In other words, the Unionists should not be denied their chance to take part in the government of Northern Ireland because the republicans have failed to abide by the Blair-Ahern terms. This is where the SDLP comes in. If Mr Hume and his deputy Seamus Mallon were to make clear that, if Sinn Fein were expelled, the SDLP would continue to serve in the executive with the Unionists, then that would complete the circle of guarantees. It would ensure that the threat of exclusion were a real penalty for Sinn Fein.

Yesterday, Mr Hume said he would not "prejudge" what would happen if Sinn Fein were expelled. He should: he should declare in advance that multi-party government would go ahead without Sinn Fein if the IRA reneges on the deal. If he does, and the Unionists say Yes, then the heat will be on Sinn Fein and the IRA to deliver disarmament, which is where the heat should be. Let Mr Hume put the republican desire for peace to the test.