But in Stormont, the agreement's first deadline slipped by without a meeting to nominate the future Justice Minister – partly because
many local politicians were in Westminster for the Prime Minister's statement.

The party leaders had been due to meet in Parliament Buildings yesterday to make nominations for the justice job but it appeared that
only the SDLP, who are unlikely to get the post, would have nominated had the meeting gone ahead. That meeting will now go ahead this morning.

Last night, the UUP party officers and MLAs met to decide their approach to the DUP-Sinn Fein document.

Afterwards, a spokesperson said: "This is an ongoing process – the UUP believes that the devolution of policing and justice is too important to get wrong. For that reason the UUP will continue to scrutinise this deal until we are in a position to deliver our verdict."

Mr Brown hailed the policing and justice deal as a "significant and defining moment" but although Tory leader David Cameron offered his full support for the deal, he warned that the SDLP and UUP must not be excluded from the process.

Mr Brown said that without the agreement, the "whole process of devolution and the peace process itself would be at risk".

"When the cross-community vote takes place on March 9, and the parties request the transfer of powers, Northern Ireland's politicians will have, by April 12, full control over their government and be able to focus on the economy, jobs, housing, public services and policing and justice."

But Mr Cameron said the agreement was between the DUP and Sinn Fein and asked what provision there was to address concerns from the SDLP and Ulster Unionists, with whom he now has an electoral alliance.

Liberal Democrat leader Nick Clegg welcomed what he described as a "very significant deal".

Calling on all parties in Northern Ireland to "work constructively together" to take forward an "agreed and practical" community relations strategy, Mr Clegg added: "A political agreement between the parties will only be durable if it is accompanied by real, concrete steps towards greater integration between the communities themselves."

Last night, Alliance leader David Ford, the man most likely to be Justice Minister, said that the DUP and Sinn Fein had been more receptive to Alliance requests for a Cohesion, Sharing and Integration (CSI) strategy, seen as the price for Alliance taking the post.

"We sought to engage (with the Office of the First and Deputy First Minister) before Hillsborough and at Hillsborough and we have been engaging with them since. We believe there are positive signs of movement over today."

In the Commons yesterday, First Minister Peter Robinson expressed a "firm and unalterable commitment to ensuring that every element of this agreement is faithfully implemented".

But he warned MPs: "We all have ways, as individual parties, of ensuring that the brakes can be put on and that things can be brought down, but only collectively can we make sure that we take them forward and that the process works."

Mr Robinson stressed that the new institutions belong to the people of Northern Ireland, and again reiterated cross-party agreement was essential to the deal progressing. "Without that we cannot move forward," he added.

Former SDLP leader Mark Durkan said: "Based on experience, the public might feel a bit more hope if there was a bit less hype."