Conservatives and Liberal Democrats are expected to join forces in the Commons next week to oppose the Blair government's controversial proposals in respect of paramilitary fugitives or "On-the-Runs" (OTRs).
The move by the two main opposition parties at Westminster increases the possibility that the Northern Ireland Offences Bill could face eventual defeat in the House of Lords, with the government then forced to use the Constitution Act to force it through.
The decision by the Conservatives and Lib Dems to coalesce on the issue also highlights a new, and potentially dangerous, period ahead for prime minister Tony Blair's conduct of the Northern Ireland peace process.
The SDLP and Alliance Party, as well as the DUP and Ulster Unionists, are also opposed to what they consider "an effective amnesty" for persons, and not just OTRs, who committed offences prior to the Belfast Agreement on April 10th, 1998.
All sides opposed Mr Blair's decision to twice postpone the Assembly elections in 2003 at the behest of the then Ulster Unionist leader David Trimble. However, this is thought to be the first time Mr Blair will have defied opposition on all fronts in pursuit of legislation favoured by Sinn Féin alone.
The second reading of the Offences Bill in the Commons on Wednesday also coincides with mounting cross-party opposition to Sinn Féin's attempt to secure British government funding for community-based restorative justice schemes.
Asked about this opposition to its approach to key issues in the North, one senior Downing Street source said: "So be it, we are building a peace process."
However, Ulster Unionist leader Sir Reg Empey has reflected unionist and SDLP concern that controversial proposals concerning policing and the criminal justice system reflect political agreements between the British government and Sinn Féin, but without the "cross-community consent" on which the Belfast Agreement was built.