The North's First Minister, Mr David Trimble, has been given an implicit assurance by the British government that devolution will not take place without the consent of the Ulster Unionist Party.
A letter to Mr Trimble from the Prime Minister's chief of staff, Mr Jonathan Powell, dated last Monday, states: "There can and will be no devolution unless it is clear that there is a viable cross-community executive in waiting to which powers can be devolved.
"If there is not, we cannot go ahead. So the anxiety that your members are yielding up their negotiating positions is wrong."
In what some sources interpreted as an implicit rebuke to dissident unionists, the letter continues: "It would be a great mistake to pass up this chance of one step forward, albeit a modest one."
The letter adds that there "appears to be a fundamental misunderstanding as to what the text we agreed [at Downing Street on May 14th] means".
"It is not supposed to be a resolution of the decommissioning issue. We cannot resolve it at present since you have made it clear that without a credible start to a process of decommissioning, there is no basis for you co-operating with Sinn Fein in an Executive; and Sinn Fein has made it clear that they do not accept prior decommissioning as a condition of entering the Executive. We cannot resolve this now."
British government sources said the leaked version of the letter which appeared in the Belfast Telegraph omitted to mention that proposals for changes in Assembly standing orders on the designation of ministerial offices were "subject to the views of other Assembly parties".
The proposed procedural cha nges would mean ministers being named but not given the "shadow" status that would entitle them, for example, to be given briefings by the British government. The amended standing orders would refer instead to "those to take up office as ministers when powers are devolved" and the nominations would lapse if devolution failed to take place by June 30th.
Sinn Fein sources made clear last night the party would resist any attempt to alter standing orders along these lines. SDLP sources said the matter would be the subject of "haggling" over the weekend. The final decision rests with the Northern Secretary, Dr Mowlam.
Commenting on the letter, a Downing Street spokesman said: "It's part of the process of clarification for the Ulster Unionists. The point this letter is making is that last Friday's proposals set out a way forward which we hope will lead to the resolution of the current impasse.
"No party is being asked to compromise on their fundamental positions and these proposals will not of themselves resolve the issue of decommissioning. You can only devolve to an Executive which is representative of both traditions and that is a guarantee all sides have had from the very outset of this process."
Meanwhile, Sinn Fein's chief negotiator, Mr Martin McGuinness, has accused Mr Trimble of "misleading the public" with his claim that he had new proposals to move the situation forward.
Asking why the UUP leader had not brought his proposals to Downing Street, Mr McGuinness continued: "He needs to end his posturing and join the rest of us in implementing the Good Friday agreement before the June 30th deadline."
The Taoiseach will discuss the current impasse with Mr Blair today. The two men will attend the FA Cup Final at Wembley Stadium this afternoon and have dinner later with their partners.
