Three former Ulster Unionist Party Assembly members, including Mr Jeffrey Donaldson, will not be returning to the party, they said today.
As Mr David Trimble's party came to terms with the decision of Mr Donaldson, Mrs Arlene Foster and Ms Norah Beare to quit the party, the three Assembly members insisted they would not be resigning their seats.
Mrs Foster told said: "We haven't taken this decision lightly, but the simple fact is we are not coming back.
"I have been a member of the Ulster Unionist party since the age of 18, and, like Jeffrey and Norah, I took this with a heavy heart. However, over the past five years, I have on occasions felt that the party no longer stood for the values which I hold dear.
Mrs Foster confirmed that she and her two Assembly colleagues had also been offered positions on the Rev Ian Paisley's negotiating team in the rival Democratic Unionist Party in the forthcoming review of the Belfast Agreement.
Mr Donaldson last night said the trio would be making a decision on where their political future lay in unionism after the Christmas holidays.
The Lagan Valley MP, who has fought a five-year battle with Mr Trimble to persuade the party to abandon its support for the Agreement and power sharing with Sinn Féin, said: "Unfortunately I have been excluded by David Trimble from his negotiating team, and I was threatened as recently as last Friday with expulsion from the party.
"I have come to the view that the Ulster Unionist Party no longer provides the vehicle for me to use my talents to achieve what I was mandated to work for.
"The meeting of the party executive last Friday was the final straw. I concluded that the party is out of touch with the views of ordinary unionists, the two thirds of the unionist electorate who reject the Agreement.
"I cannot see how the UUP could ever be the majority party in Northern Ireland or provide the leadership that is required, certainly under David Trimble's leadership."
An Ulster Unionist Party statement last night said the decision of Mr Donaldson to resign was "a matter of regret", but not a surprise.