Ulster Unionist Jeffrey Donaldson has said the current crisis in the peace process is a direct result of flaws in the 1998 Belfast Agreement.
In an interview at the UUP's headquarters in east Belfast today Mr Donaldson said "The agreement, in my opinion, was not enough to deliver a real and lasting peace...and the history of the agreement has been marked by crisis after crisis,"
"It has not been a recipe for political stability -- the government is suspended at the moment, terrorist activity on the loyalist side is on the increase, and republicans have failed to decommission any further weaponry."
Donaldson walked out of talks on the eve of the signing of the agreement, protesting the deal did not secure decommissioning, and since then has been seen as the standard-bearer of the party's anti-agreement faction.
"The agreement itself is aspirational, and the biggest flaw is its failure to link political progress with progress for disarmament of terrorist organisations and the ending of their activities," he said.
"I say unashamedly that the flaws I pointed out in 1998 have proven to be the Achilles heel of the agreement."
Although seen by many as a possible replacement for Trimble at the head of a party whose grassroots are increasingly sceptical about the Good Friday Agreement, 38-year-old Donaldson has not so far made a direct challenge for the leadership.
Nonetheless it was pressure from Donaldson, one of six UUP members of the British Parliament, which forced Trimble in September to adopt and more hard-line stance on disarmament in a prelude to the current crisis.
"The stakes are extremely high...I believe this is the most serious crisis yet to confront the peace process in Northern Ireland and I do not believe that its resolution will be an easy one," said Donaldson. Twice since October 2001 the IRA has helped break a logjam in the political process by destroying part of its substantial arsenal in secret, witnessed by international arms monitors.
Now unionists are calling for public acts of disarmament and the total disbandment of the IRA, which called a second ceasefire in 1997.
"People say 'you've increased the level of the bar' - yes we have, because the IRA have increased the level of their activity at a time when they should have been reducing it," said Donaldson.
Asked how the current stand-off could be ended, he added: "I think the IRA, first of all, would have to make a very clear public declaration that the war, in their terms, was over, that there was no longer any requirement for their organisation.
"They would have to give a clear timescale within which the organisation was to be wound up, and on top of that there would have to be clear evidence that each of the IRA's units, brigades or whatever you want call them, have been disbanded."
Donaldson said an independent monitoring mechanism - backed by security assessments from the police and the British Army - would be needed to verify the disbandment of paramilitary groups.
"I am not in favour of bringing people from the international community in," he added.
Sinn Fein rejects the focus on the IRA at a time when the majority of violence in Northern Ireland is coming from loyalist paramilitaries. The IRA issued a statement yesterday saying the process was under threat from loyalist and militarist elements within the British Army.