Lord Molyneaux is now believed among those likely to defect if the Ulster Unionist Party finally splits over the issue of Sinn Fein's membership of the new Northern Ireland Executive.
The news will shock the party hierarchy as Mr David Trimble, Northern Ireland's First Minister-designate, comes under growing pressure to seek Sinn Fein's exclusion from office following the RUC's confirmation that it suspects Provisional IRA involvement in the murder of Mr Andrew Kearney.
Usually reliable sources told The Irish Times last night they believed at least four Ulster Unionist MPs are prepared to quit the party if Mr Trimble enters the Executive with Sinn Fein without the prior commencement of the decommissioning of IRA weapons, a commitment to the dismantling of its paramilitary structure, and the declaration that its "war" is over.
The sources said that in that event Lord Molyneaux, who resigned the leadership three years ago, would feel "honour-bound" to resign his post as patron of the ruling Ulster Unionist Council. And they confirmed their expectation that Lord Molyneaux's successor as MP for Lagan Valley, Mr Jeffrey Donaldson, and the DUP's deputy leader, Mr Peter Robinson, would then prove pivotal in bringing about a "realignment" within unionism, embracing rebel Ulster Unionists, the DUP and the UK Unionist Party.
Confirming earlier Irish Times reports that realignment is firmly on the agenda of anti-Agreement unionists, the sources also made it clear that Lord Molyneaux continues to hold sway with his former MPs.
It is understood he was consulted last week before four of the UUP's MPs decided to defy Mr Trimble and vote against "the principle" of the Northern Ireland Bill in last Monday night's vote on Second Reading.
Mr Trimble voted for the Bill - which brings the Northern Ireland Assembly and the other institutional structures set out in the Belfast Agreement into being - as did his deputy, Mr John Taylor.
But the scale of the continuing Ulster Unionist crisis - and the rising challenge to Mr Trimble's authority - is underlined by Mr Taylor's warning, repeated in terms three times during last week's Commons proceedings, that he might actually vote against the Bill at Third Reading on Friday.
Mr Taylor last night confirmed that he would make a final decision after hearing the British government's response to his concerns about the mechanisms for excluding from office people not sustaining a commitment to purely peaceful methods at the Report Stage on Thursday. The Committee Stage of the Bill continues this afternoon.