Mr David Trimble will seek re-election as leader by the Ulster Unionists' ruling body next month in defiance of a call for his resignation by a fellow MP.
Mr Trimble said yesterday he considered it his duty to stand for the leadership of the UUP despite Mr David Burnside's appeal for him to stand aside in favour of someone who can reunite the party and re-establish it as the largest unionist party.
Mr Burnside dismissed his party leader as a divisive and failed figure.
The South Antrim MP, made his resignation call at Stormont yesterday, prompting speculation that another candidate may emerge in time for a leadership contest on March 27th.
The party constitution demands that the leader seek re-election each year at the agm of the ruling Ulster Unionist Council.
Mr Burnside challenged Mr Trimble: "Having consulted across the party in recent weeks, it is clear David Trimble has lost the confidence and trust of the majority of the Ulster Unionist Party membership.
"There is a sea change in opinion throughout the membership.
"Members and supporters want a UUP leadership team that will unite and restore the party to its position of dominance within unionism once again."
In the most forthright attack on the UUP leader, Mr Burnside added: "He is perceived to have failed to deliver for unionism. He is blamed by the majority of unionists for abandoning the UUP's pledge of 'no guns, no government', and for failing to protect the proud title of the RUC.
"The vast majority of unionist voters also have no confidence in him as a negotiator. They also see him as having become totally detached from unionist grassroots opinion." He accused Mr Trimble of providing only "managerial incompetence and electoral decline". Mr Burnside, who resigned the party whip last June along with Mr Jeffrey Donaldson and the Rev Martin Smyth over the party stance on the Belfast Agreement and the Joint Declaration, also launched a tirade against Mr Trimble's handling of the disciplinary action against the three.
He dwelt on the high court challenge to the action which cost the party £80,000. He also blamed Mr Trimble for the tension in the relationship between the party and "our traditional friends and allies" in the Orange Order, and was severely critical of the party's Assembly election campaign. They said the party was "more liberal" than the pro-agreement Alliance Party.
Calling for a new and united leadership team to take over, Mr Burnside concluded: "It is amazing, if not almost inconceivable, that a leader who has led the party through failure after failure in the last three election campaigns should be considering submitting his name for another year at our agm at the end of March. If our leader is to be judged on performance then he should go immediately."
Mr Trimble was unavailable for comment but a party spokesman said he considered it his duty to offer himself for re-election at next month's meeting. The Irish Times was told Mr Trimble is confident he will still lead the party after the agm.
Before publicly calling on the leader to stand down, Mr Burnside had attended a meeting at headquarters of the party's liaison group which includes MPs and Assembly members, at which "there were heated exchanges".
However, it is understood that a "solid majority" of those present backed Mr Trimble and were critical of the stance taken by Mr Burnside.
There is speculation that his comments are designed to encourage another senior party member, possibly Sir Reg Empey, to stand against Mr Trimble next month. He was unavailable for comment yesterday.
Lord Kilclooney, the former Mr John Taylor, is thought not to be a likely leadership candidate.
One source suggested yesterday that the heave could be the "last hurrah" for the anti-Trimble element within the party after a series of failures.
Mr Jeffrey Donaldson, who last month defected from the Ulster Unionists to the DUP, said he shared Mr Burnside's assessment of Mr Trimble. "I fear for the Ulster Unionist Party that a leadership change may be too late to restore their integrity," he said.