Mr David Trimble last night warned the Secretary of State, Dr John Reid, that the political process in Northern Ireland "is in serious danger of imploding."
At a meeting in London the First Minister and Ulster Unionist leader pressed Dr Reid for government action in the light of recent revelations and allegations about continuing IRA activities in the United Kingdom and abroad.
It is likely that Dr Reid and the Prime Minister, Mr Tony Blair, will comment on the current state of the IRA ceasefire during questions in the House of Commons this afternoon.
However, there is no indication that London is at present prepared to consider sanctions against Sinn Féin.
Such sanctions could come in the form of the party's exclusion from ministerial office or a decision to "specify" the IRA in a move which unionists argue could see released prisoners taken back into custody.
Whitehall sources insisted last night that prisoners could only have their licences revoked on an individual basis in the light of evidence by the police about activities in breach of the terms of their release.
Mr Trimble's focus on possible action over prisoners - and on the possibility that the IRA might be encouraged to engage in public acts of decommissioning - is seen in Whitehall as evidence of his continuing desire to defuse the threatened political crisis and to avoid meltdown in the political institutions established by the Belfast Agreement.
However, the First Minister told Dr Reid that recent revelations about republican intelligence-gathering activities, continued questions about the St Patrick's Day break-in at the Castlereagh police complex, and US congressional allegations about the IRA's international terrorist connections meant "the leeway for unionists in the present situation is very limited."
Following last night's talks Mr Trimble told The Irish Times he agreed with the Taoiseach, Mr Ahern, that "the solution in the long term requires republicans to grasp the nettle of disbandment."
The commitment to exclusively peaceful and democratic means, he said, "means that there can be no private armies."
However, he added that that longer-term remedy offered no solution in the immediate situation and he was pressing for British government action "not least because republicans are doing nothing to restore their own credibility and commitment".