The appointment of the international Independent Monitoring Body (IMB), regarded by London and Dublin as a crucial element in efforts to restore the Northern Ireland Assembly, could be delayed until September.
This became clear last night amid signs of increasing British confidence that it will be able to reassure doubtful Ulster Unionists that the IMB will not give Dublin a direct role in the Assembly's internal affairs.
Whitehall sources confirmed that the British government would still like to see the early establishment of the body, which will be asked to monitor paramilitary and political "acts of completion" as part of any deal enabling the resumption of devolved government in the North.
The hope had been that the appointment of the four-member body, drawn from Britain, Northern Ireland, the United States and the Republic, ahead of the summer break would give added impetus to a fresh drive by the British and Irish governments to hold the postponed Assembly elections in October.
However, sources said a delay in confirming the final list of nominees meant the odds were probably 40-60 against an announcement next week, with a consequent delay until next month increasingly likely.
It is understood the terms of a new international treaty bringing the IMB into being have been concluded, and could be published if the composition of the body was agreed, so allowing for an announcement within a week or so.
However, Westminster MPs are unlikely to see the draft British legislation until the House of Commons resumes for two weeks in September ahead of the party conference season.
The proposal for an international body was developed during the Hillsborough talks this year.
It came in response to Mr David Trimble's demand for an independent element in the monitoring of paramilitary ceasefires during the debate about "sanctions" to be deployed against any party in breach of its commitment to exclusively peaceful and democratic means.
The proposal, however, has rebounded on the embattled Ulster Unionist leader, prompting fears in London and Dublin that this is a second issue - in addition to the proposed disciplinary action against the three UUP MPs who resigned the party whip - on which Mr Trimble could face a defeat at the Ulster Unionist Council in the autumn.
Dublin is said to be sensitive to Mr Trimble's difficulties on the issue and to have been helpful in behind-the-scenes negotiations seeking to define the remit of the IMB in a way which might reassure unionist critics of the plan, such as Lord Kilclooney (formerly Mr Trimble's deputy and Strangford MP, Mr John Taylor).
Lord Kilclooney appeared to harden his opposition to the proposal on Thursday and is thought likely to change his position only if the body, complete with its Dublin nominee, is appointed by the British government alone.
The Irish Times understands the four members will be appointed jointly by London and Dublin, in line with the practice adopted for the International Commission on Decommissioning headed by Gen John de Chastelain.
However, the suggestion is emerging that, while the four members would jointly assess the relevant intelligence and determine whether a ceasefire breach had occurred, a sub-group of the body, possibly comprising only the British and Northern Ireland members, might be responsible for recommending to the Assembly what sanction should be applied against any party or individual concerned.
In a further attempt to reassure unionists, it is being stressed by London that the four members, while nominated by their governments, would act independently.
It is also implied that the British Secretary of State would, at least technically, enjoy a power of unilateral action as a result of the legislation creating the IMB.
Under the agreement, concluded by the British Prime Minister, Mr Tony Blair, and the Taoiseach, Mr Ahern, last April, it would be for the Assembly in the first instance to act on sanctions following any finding by the IMB.
In the event of an Assembly failure to do so, it would then fall to the Secretary of State, in consultation with the Irish Government, to provide a solution consistent with the IMB's original recommendation.
However, the line in Whitehall is that "consultation" does not necessarily mean "agreement", with the example that London consulted Dublin about the postponement of the Assembly elections before proceeding to postpone despite the Irish Government's opposition.