The Government will withdraw its plans to grant pardons to paramilitary fugitives - so-called on-the-runs - if British legislation on the same issue is not enacted.
This was confirmed last night after Sinn Féin announced the withdrawal of its support for a bill currently before the House of Commons, which would allow paramilitaries and others suspected of terrorist offences to return to Northern Ireland without facing court proceedings.
The Northern Ireland Office (NIO) said the Sinn Féin change of position would not mean the bill would be withdrawn.
An NIO spokesman said: "There is no other vehicle for dealing with OTRs, and Sinn Féin is deluding itself if it thinks there is."
In Dublin, a spokeswoman for the Government said Irish measures to deal with OTRs would not proceed if British legislation was withdrawn.
"This was an initiative that was always going to be done in parallel with the British government," she told The Irish Times. "If the British government does not proceed, then neither will the Government."
Sinn Féin vice-president Pat Doherty claimed the current British proposals, which cover British soldiers and police officers as well as paramilitaries, were "far removed" from what was agreed with the British government in talks at Weston Park in 2001.
The West Tyrone MP accused London of "sleight of hand" over the Bill's inclusion of crown forces suspected of crimes connected with the Troubles before 1998.
Sinn Féin welcomed the British initiative when the Bill was published early last month. However, Mr Doherty said yesterday the party's current position followed consultation with those on the run who cannot return for fear of arrest.
The SDLP insisted its opposition to the OTRs legislation and relentless campaigning had forced Sinn Féin's hand. The party called for the Bill to be dropped.
The SDLP's Alex Attwood said Sinn Féin should have known since 2003 that the British would include all suspected of terrorist crimes, quoting details of a paper published at the time to support his claims.
SDLP leader Mark Durkan has repeatedly claimed that republicans and the British government have been colluding, with each helping the other to "cover up their dirty secrets".
Unionists also called for the abandonment of the Bill.
DUP deputy leader Peter Robinson said: "There is now no excuse to pursue a Bill that is utterly unacceptable to all right-thinking people. Representatives from Northern Ireland who sat on the committee scrutinising the Bill have been united in their opposition to this judicial farce."
UUP leader Sir Reg Empey concurred: "[ This legislation] should be scrapped, and the government should not attempt to renegotiate with Sinn Féin another even worse piece of legislation."
Prime minister Tony Blair and Northern Secretary Peter Hain have maintained it was inconceivable that paramilitary fugitives would be given what amounted to an amnesty, while crown forces members were forced to undergo due process.