Mr David Trimble is believed to be ready to put his political life on the line in a last-gasp attempt to persuade his party to restore the power-sharing Executive on the basis of the IRA's offer to put weapons beyond use.
However, a decision to go ahead with Saturday's meeting of the Ulster Unionist Council appeared to be in the balance last night, amid reports of growing opposition within the UUP Assembly Party and with deputy leader Mr John Taylor still holding out against the deal.
After a further meeting with the Prime Minister, Mr Blair, in London yesterday afternoon Mr Taylor indicated that he was unimpressed with British government positions on flags and policing.
Mr Trimble is expected to talk with Mr Taylor this morning, ahead of a meeting of his Assembly Party at Stormont. Sources said solid backing would be necessary if Mr Trimble is to persuade party officers at their meeting tomorrow not to cancel, or at least postpone, Saturday's meeting. It is understood some of Mr Trimble's closest allies in the Assembly are among those urging postponement of any decision on whether to re-enter government.
The UUP leader was reportedly happy with an assurance from Mr Blair in the Commons that the opening of IRA weapons dumps to inspection would be but "a first step" in a process which would eventually see weapons "completely and verifiably put beyond use".
Mr Trimble asked Mr Blair what "beyond use" meant and to confirm that "we wish to see proper decommissioning taking place within the terms of the legislation for it".
Mr Blair replied: "The dumps are an important confidence-building measure but not a substitute for the full action that needs to be taken under the legislation. And the reference to `beyond use' . . . of course, in the legislation itself there is a reference to things being permanently unusable."
Earlier, Mr Trimble heard the Northern Secretary, Mr Mandelson, give an assurance that "there has been absolutely no agreement or understanding with the Irish Government" to the effect that he had agreed never again to suspend the Executive.
However, Mr Trimble won no advance on the Police Bill. Mr Mandelson said the name of the police should be judged against two of Patten's objectives - that the RUC should not be disbanded and that the police service attract recruits from all parts of the community.
"I believe the sensible way forward is to provide a legal description in the Police Act which incorporates the Royal Ulster Constabulary - in effect the title deeds of the new service - while introducing a new name that will be used for all working and operational purposes. The Police Service of Northern Ireland is the best suggestion made so far."