Exchanges between the Northern Secretary, Mr Mandelson and Mr David Trimble in the House of Commons this afternoon could determine whether the Ulster Unionist leader will recommend his party council's acceptance of the IRA's "weapons beyond use" offer at its meeting on Saturday.
The nervous expectation of both governments is that he will. However, sources say a final decision might not be made before a resumed meeting of UUP officers on Friday morning, and it is unclear if Mr Trimble's deputy, Mr John Taylor, is prepared to back such a move.
Mr Taylor described a letter from Mr Mandelson to Mr Trimble on Monday night as "devoid of decisions" on key unionist demands on policing and the flying of the Union flag on government buildings. When asked if he thought Saturday's meeting would go ahead as planned, Mr Taylor told BBC Radio Ulster: "I personally thought calling the meeting was somewhat premature, that we would have to get some of these things sorted out successfully."
The British government yesterday published the Police (Northern Ireland) Bill to implement the Patten proposals for reform of the RUC. As expected, the Bill defers a decision on the new title of the police service, pending future consultation between the Secretary of State and the parties sitting on the policing board, which will replace the present police authority.
Mr Trimble is expected to press Mr Mandelson on his preferred form of title during Northern Ireland questions this afternoon. However, faced with a growing chorus of nationalist and republican criticism over his failure to confirm his earlier decision - that the force would be renamed "The Police Service of Northern Ireland" - there is little expectation that Mr Mandel son will feel able to give Mr Trimble a firm assurance that "RUC" will be incorporated, or otherwise retained, in the formal title.
Mr Trimble's difficulty on the policing issue was starkly underlined by a statement from Mr Andrew Mackay, the Shadow Northern Ireland Secretary, declaring: "We find it deeply regrettable that the Bill does not contain provision for retaining the proud name of the Royal Ulster Constabulary."
The 64-page Bill is likely to receive its second reading from MPs next week and is expected to reach the statute book by the end of the summer. Other key provisions cover 50/50 recruitment of Catholics and Protestants to correct the present imbalance, a new declaration or oath for new recruits, and the appointment of an independent police ombudsman.
The Minister for Foreign Affairs, Mr Cowen, said in a statement last night that, while he welcomed the Bill as "another step" on the road to implementing the Patten recommendations, "the Government remained committed to the full implementation of Patten".
However, Mr Cowen added: "On a preliminary assessment, certain aspects of the Bill give cause for concern, because they carry the risk that the new service will not succeed in winning the level of cross-community support that will be necessary to create a new beginning. It is essential that all such issues be resolved in the context of the legislative process."
A Government source said Mr Cowen was signalling concern about the future police service in Northern Ireland, but was not suggesting that the Bill would in any way affect the IRA's position, announced on May 7th.