The Rev Ian Paisley and Gerry Adams will have to strike their own devolution deal if next week's powersharing deadline in Northern Ireland is missed, Peter Hain said today.
Both leaders have until Monday to sign up to an agreement to go into government linked to a multi-billion economic package.
But with the DUP still holding out on a commitment, the Northern Ireland Secretary claimed the parties would be on their own if they failed to meet the deadline.
As Mr Adams prepared to meet Taoiseach Bertie Ahern in Dublin, Mr Hain warned those in the DUP who believe they can push past the March 26th deadline that the party will lose everything it gained at the St Andrews talks if there is no devolved government.
"March 26th is cast in stone," he said. "It is cast in statute, whether anyone likes it or not. My one big fear is that people think there is a way back after midnight on March 26th.
"There will not be. There will be no emergency Bill after then, and Jack Straw has reinforced that in the House of Commons.
"The Assembly will close down, the salaries will stop, the allowances will stop. Water bills are being processed over the next week and those will kick in.
"We will also not be facilitating any party discussions. The DUP and Sinn Féin would have to find their own way to agree a cast-iron deal and then come back to us," Mr Hain said.
"This isn't just me saying this. I would not have taken the stance I have on the deadline without clearing my lines first with the prime minister and after March 26th he is not going to come back for second helpings."
Mr Hain will have to know by midnight on Saturday that Mr Paisley and Sinn Féin's Martin McGuinness will be nominated as Northern Ireland's next First and Deputy First Ministers if he is to make the restoration order next Monday to bring back devolved government.
The decision will hinge on the outcome of a meeting of the DUP executive on Saturday. The DUP wants clarity from Sinn Féin that its recent endorsement of the Police Service of Northern Ireland is not equivocal and that it is being matched by co-operation on the ground in republican neighbourhoods.
The party will also be heavily influenced by the multibillion-pound economic package Chancellor Gordon Brown will propose on Thursday to bolster the new power-sharing government.
The North's parties have been arguing Mr Brown will need to significantly improve on the offer he made last November of £50 billion over 10 years if the next Stormont government is to tackle key infrastructural problems.