The British Prime Minister, Mr Tony Blair, and the Conservative leader, Mr Iain Duncan Smith, will discuss the state of the IRA ceasefire at a Downing Street summit this morning.
Allegations that the Provisionals have recently purchased Russian assault rifles, together with last Friday's revelations about republican intelligence-gathering and the investigations into the break-in at Castlereagh, are also expected to dominate separate talks later in the day between Mr Blair and Northern Ireland's First Minister, Mr David Trimble.
British sources last night dismissed a report in yesterday's Sunday Telegraph that the Provisionals had acquired at least 20 AN-94s in a deal detected by the Russian security services. They specifically denied cabinet ministers, or senior Northern Ireland politicians, had been briefed on this by British military intelligence.
While maintaining it was of no particular security significance, the sources said that evidence republicans had recently upgraded intelligence held on senior Conservative politicians was "of a higher order of concern, at least in political terms."
The indications were that Mr Trimble's response to recent developments would be dictated by the overall government and police assessment that there is no evidence that the IRA is planning to resume a military campaign. However, as they face into their Assembly election year, some pro-Agreement unionists are pressing for a tougher line with Sinn Féin.
Mr Fred Cobain, MLA for North Belfast, said at the weekend it would be "immoral" to ask unionists to sit in government with Sinn Féin if republicans were continuing to target senior British politicians and military establishments. Meanwhile, Mr Jeffrey Donaldson MP moved a successful resolution at a meeting of the UUP executive on Friday night which well-placed sources have told The Irish Times could lead - pending a final adjudication on responsibility for the Castlereagh break-in - to the reimposition of Mr Trimble's bar on Sinn Féin participation in meetings of the North/South Ministerial Council.
British officials were working to counter the apparent fresh threat to the stability of the political process in Northern Ireland.
Mr Duncan Smith requested his meeting with Mr Blair on Friday night after the disclosure that senior Conservatives featured on a list found by detectives in Belfast in the course of investigations into the Castlereagh break-in.
The Conservative leadership, like those named on the list, was only informed on Thursday last in anticipation of news of the discovery breaking on the BBC.
British sources said the Home Office was informed soon after the discovery and that the security services concluded there was no increase in the level of threat and no need to change security measures already in place in respect of some of those named.
A senior Conservative source last night said he found this incredible: "Even if they thought there was no increased threat, you would at least have expected them to inform the people concerned. And of course, in the wider context, you have to ask why these people are continuing to gather such information at all."