The threat posed by dissident republicans is expected to top the agenda in planned summit talks between the British Prime Minister, Mr Blair, and the Taoiseach, Mr Ahern, within two weeks.
This became clear yesterday as senior British sources confirmed the Prime Minister's "increasing concern" about the "Real IRA's" capacity to coalesce with other breakaway republican groups opposed to the Belfast Agreement.
A security alert caused disruption in the Kings Cross area of London yesterday morning as rail and tube services otherwise returned to normal. Alerts following Wednesday's bomb attack on a track near Ealing Broadway station in west London forced the closure of other stations, causing disruption to tens of thousands of commuters.
The attack was regarded as an attempt to disrupt a pageant to celebrate the Queen Mother's 100th birthday. The device was believed to have contained half a kilogram of high explosives.
Authoritative British sources confirmed the government's growing anxiety about the increasing cohesion of, and the increased numbers of people involved in, dissident republican attacks on the peace process.
Official sources did not disagree with independent estimates that 140 to 160 people may now be involved in the dissident republican campaign. The sources stressed that co-operation between the security forces in Britain and Ireland remained of the highest order, but there is clear anxiety that Mr Blair and Mr Ahern should review the situation urgently.
The dissident threat was discussed this week by the Northern Ireland Secretary, Mr Peter Mandelson, and the Minister for Justice, Mr O'Donoghue, and will dominate talks next week between the Minister and the Home Secretary, Mr Jack Straw.
Mr Mandelson is also scheduled to meet the Minister for Foreign Affairs, Mr Cowen, in London next week, to discuss outstanding points of difference between the two governments on the Police (Northern Ireland) Bill implementing the Patten reforms of the RUC.
However, there appears to be a question mark over whether that meeting will proceed before the summer break, following discussions between senior Irish and British officials on the issue in Downing Street last Monday.
The Police Bill, with some 60 amendments made in direct response to pressure from the SDLP, is due to receive its Second Reading in the House of Lords next week. The Lords Committee Stage of the Bill will be resumed in September, and the Bill will be returned to the Commons to consider any further amendments in the "spillover" period in October before the opening of the new parliamentary session.
It seems unlikely that the British government will decide much before then the terms of any amendment defining the "operational purposes" of the newly-named Police Service of Northern Ireland.
Meanwhile. Senator George Mitchell, the former chairman of the talks process, has again said progress toward peace in Northern Ireland is "irreversible".
Addressing the American Bar Association in London, Mr Mitchell said: "We are seeing the difficulties of implementation. As most of you saw (on Wednesday) there are dissident groups on both sides who are unreconciled to peace and remain committed to the use of violence to advance their political objectives." He continued: "There will undoubtedly be setbacks along the way, but I believe the path towards peace has been set irreversibly in Northern Ireland."