The Ulster Unionist leader, Mr David Trimble, has insisted that the Belfast Agreement is the political way forward despite the unrest and division within his party.
Unionists had to choose between being inclusive or hostile and suspicious, he said.
Mr Trimble described as "completely without foundation" the claim by dissident MPs Mr Jeffrey Donaldson, Mr David Burnside and the Rev Martin Smyth that his policy was acquiescence to the destruction of the union by stealth.
He also said that if republicans illustrated that their war was over a majority of unionists would stand by the agreement.
In one his strongest recent endorsements of the agreement Mr Trimble said the consent principle of the Good Friday accord had in fact strengthened the union, and warned that following the leadership of the three MPs could destroy the union.
"I do regard the agreement we entered into as strengthening the basis of the union because it brought for the very first time the recognition by all parties in Northern Ireland, and the Irish Government and the Irish people, of the consent principle - a recognition of the legitimacy of the union by others.
"And that has been respected over the course of the past five years in a way that it would not have been before," said Mr Trimble.
He warned unionists against retreating into a hostile form of unionism. "Withdrawing to a form of unionism that is exclusive, that retreats into the laager and draws the tents around, and doesn't try to broaden and be inclusive is actually a greater threat to the union," he told BBC Radio Ulster on Saturday.
Mr Trimble empathised with a London Times editorial of last week which contended that if unionists followed the line of the three MPs who resigned the party Westminster whip, it would lead to "Sinn Féin laughing all the way to a united Ireland".
"That is the different fundamental approach between a unionism that is realistic and that addresses the reality of the situation, that presents its case reasonably, that tries to broaden support for the union and for the Northern Ireland political institutions, and a unionism that is suspicious, hostile to others and the unknown and reluctant to engage," said Mr Trimble.
He also addressed his opponents' claims that the UUP could be destroyed in Assembly elections if it continued to stand by the agreement and failed to reject the declaration flatly. He said unionists had a complex, "nuanced" view of the current situation, and that was clear from the polls and the findings of UUP focus groups.
The polls showed that if there was a referendum on the agreement today only 37 per cent of unionists would vote yes. But if "republicans said the war was over", then that figure would increase to over 50 per cent, and if republicans fully abided by the agreement and decommissioned and disbanded, then around 75 per cent of unionists would endorse the agreement.
"As to the position of the electorate that is nuanced, but it is clear that they want this to work," said Mr Trimble. The three MPs' argument that this complex view signalled that unionism had retreated to "a negative, rejectionist unionism" was a mistake.
Mr Trimble said that despite the suspension of the three MPs from the UUP on Thursday he wanted them to remain in the party, "but as members of the party supporting the party and its policies".
"They need now to draw back from the brink and to think again. I want to repeat that again and again. There is no need for this lemming-like rush to the edge."
