The Ulster Unionist Party's Mr Jeffrey Donaldson is understood to be considering his political future after he lost a challenge to Mr David Trimble last night.
Mr Donaldson had proposed a motion calling on delegates to reject the Joint Declaration on the Northern Ireland peace process that was published by the British and Irish governments last month.
Following the vote at a meeting of the 809-member Ulster Unionist Council last night, which Mr Trimble won by 440 votes to 369 (54 per cent to 46 per cent), the party leader urged Mr Donaldson not to carry out his threat to walk away from the party.
But the Lagan Valley MP refused to disclose whether he will leave the UUP and bring his supporters with him. Mr Donaldson said he was going to consider his future in the partyonce he had faced down a motion of no confidence against him in his ownconstituency.
Mr Donaldson was expected to leave the party with a number of colleaguesincluding the UUP honorary secretary Ms Arlene Foster.However some prominent anti-good Friday agreement Ulster Unionists were likelyto remain in the party including the South Antrim MP Mr David Burnside.
At a press conference following the vote last night, Mr Donaldson described the vote as a "Pyrrhic victory" for Mr Trimble, claiming the delegates had a choice of voting for "principles or a tactical approach to this process that has not served this party well" and ended up choosing tactics above principle.
"We will decide whether this party represents the best way forward for unionism, but I have to say to you very honestly the decision taken tonight leaves me with a very serious doubt about whether the Ulster Unionist Party represents what I joined it for - represents what the people who voted for me, voted for," he said.
"Perhaps my energies will be better employed in other ways."