The Ulster Unionist Party leader, Mr David Trimble, may have lost the support of a majority of his parliamentary party before the end of the week, opponents of Friday's Northern Ireland Agreement claimed last night.
Senior party sources said the likely rejection of the deal by the Grand Orange Lodge on Wednesday could have a major influence on the outcome of next Saturday's all-important meeting of the 800member Ulster Unionist Council in Belfast.
While Mr Trimble is confident of winning, and his opponents would not forecast the meeting's outcome, an MP said it was "certainly conceivable" the party leadership could lose the vote.
Attention is beginning to focus on the position of the South Belfast MP, the Rev Martin Smyth, who is due to return to the North from Australia tomorrow or Wednesday.
Mr Smyth holds a pivotal position within the 10-strong parliamentary party, five of whom - Mr William Ross, Mr William Thompson, Mr Roy Beggs, Mr Clifford Forsythe and Mr Jeffrey Donaldson - are declared against the agreement.
The former party leader, Lord Molyneaux, is also understood to be opposed to the agreement.
Party sources last night insisted he would play no public part in opposing Mr Trimble but one anti-agreement MP said: "He'll have to."
After conflicting reports over the weekend, it was confirmed last night that Mr Donaldson did vote against the agreement at Saturday's meeting of the UUP executive committee.
While the leadership yesterday declared itself happy with Mr Trimble's 55-23 win, the margin was less comfortable than Mr Trimble had expected.
His opponents claimed it would have been still closer had delegates, including those committed to a meeting of the Orange Order's central committee, not left before the vote.
On the BBC recently, Mr Trimble acknowledged a two-to-one split within unionism generally over the talks process, but assessed the position within his own party at 80-20 per cent in his favour.
It also emerged last night that pro-Trimble members forced Saturday's vote by a show of hands, which Mr Trimble's opponents claimed may have further distorted the picture, with some delegates feeling obliged to back the leader in public.
The anti-agreement faction is determined that Saturday's vote will be by secret card ballot.
It is thought unlikely that Mr Donaldson or Mr Smyth would back any move to strip Mr Trimble of the leadership of the parliamentary party, thereby taking the party back to the position which obtained from 1974 to 1979 when Mr Molyneaux led at Westminster while Mr Harry West remained the leader of the party in the North.
And the loss of a majority within the parliamentary party itself would not necessarily reflect the mood in the party as a whole. Mr Trimble, after all, was elected leader by the UUC without the support of a single fellow MP.
If Mr Smyth breaks with Mr Trimble, however, that would mean nine pro-Union MPs (including the Rev Ian Paisley, Mr Peter Robinson and Mr Robert McCartney) lined-up against the agreement, with just four - Mr Trimble, Mr John Taylor, Mr Ken Maginnis and Mr Cecil Walker - in favour.
Anti-agreement MPs acknowledge at this stage that the unionist split is unlikely to prevent a Yes vote in the referendum.
However, the real implications of it will become apparent as constituency parties begin selecting candidates for the Assembly elections, and the battle is joined by the two sides for dominance within it.
