Mr David Trimble has asked Mr Tony Blair to order the Northern Ireland Office to fully consult his party about the content of an imminent report on the "normalisation" of security arrangements and practices in the North.
The First Minister wrote to the British Prime Minister requesting his intervention after a highly acrimonious meeting he and his colleague Mr Ken Maginnis MP had with the North's security minister, Mr Adam Ingram, on the issue at Stormont on Tuesday.
The "normalisation" report - promised on Good Friday in anticipation of "the development of a peaceful environment" on the basis of the Belfast Agreement - is eagerly awaited in nationalist and republican circles, as well as by the Irish Government.
British sources say the report, which could be published early this month, will be "indicative" in nature, outlining measures which could be taken consistent always with the ongoing assessment of the level of terrorist threat in Northern Ireland.
However, while apparently unrelated to any other matter, the clear hope in some political and official circles is that the report could impinge on republican calculations as crunch decisions on the issues of decommissioning and the creation of the Northern Ireland executive draw ever closer.
Unionist suspicions about the nature and purpose of the proposed report have been fuelled by the NIO's apparent unwillingness to consult them about the content.
Mr Ingram reportedly infuriated Mr Trimble and Mr Maginnis by telling them that government did not normally consult "the opposition" about the development of "strategy" and that he would consult them and other parties only on matters concerning "implementation".
In his letter to the Prime Minister of last Wednesday, Mr Trimble apparently expresses surprise at being considered part of "the opposition", rather than as a participant "in a joint enterprise".
The Ulster Unionist leader also argues strongly that the wording of the Belfast Agreement requires the Northern Secretary and her ministers to "consult regularly on progress [towards normalisation], and the response to any continuing paramilitary activity, with the Irish Government and the political parties, as appropriate".
There is apprehension in some unionist circles about the British government's review of the legislation regulating and controlling private firearms in Northern Ireland. And unionist MPs of all parties are certain to resist any proposals to dramatically reduce the number of personal protection weapons before decommissioning by the IRA begins and without a clear assessment by security chiefs that the threat of terrorism from other organisations has ended.
However, the immediate focus of Ulster Unionist concern is the British government's evolving attitude to permanent patrol bases, the fortified bases along the Border. While happy to see some of these "mothballed", Mr Maginnis insists any decisions must be swiftly "reversible" in light of any emergent terrorist threat. And he says any decision to dismantle them in the medium term would show "a very poor perception of the fear that exists still in Border communities".
The Belfast Agreement says: "The British government will make progress toward the objective of as early a return as possible to normal security arrangements in Northern Ireland, consistent with the level of threat and with a published overall strategy, dealing with 1) the reduction of the numbers and role of the armed forces deployed in Northern Ireland to levels compatible with a normal peaceful society; 2) the removal of security installations; 3) the removal of emergency powers in Northern Ireland; and 4) other measures appropriate to and compatible with a normal peaceful society."
Mr Maginnis told The Irish Times last night: "I want to see a report on everything that has been done so far, illustrative of a strategy, and showing where the balance has been observed."