Gordon Brown and Brian Cowen, his Irish counterpart, were flying to Belfast early this morning to set the seal on an historic deal between Sinn Féin and the Democratic Unionists to share full power.
London last night hailed the agreement, which will see policing and criminal justice powers devolved to Northern Ireland, as the final piece in the jigsaw after a search for peace lasting nearly 20 years.
The two prime ministers, who held three days of intensive talks at Hillsborough Castle, Co Down, with the parties last month, will jointly chair a plenary session this morning to formalise the deal.
The breakthrough came late last night when Peter Robinson, the DUP leader who has been involved in 10 days of talks with Sinn Féin, declared he had the full backing of his party in the Stormont assembly.
Robinson had faced the threats of resignations – and defections to the hardline Traditional Unionist Voice party – from a core of members who balked at giving Sinn Féin a say over policing. Up to 14 members of the DUP's 36-strong assembly team were said to be opposed to a deal.
In a two-hour meeting with his party at Stormont last night, Robinson persuaded the doubters that he had secured assurances in two key areas. First, the parades commission, seen by many Unionists as biased against Orange parades, would be reformed. Second, that Sinn Féin would not be able to dictate to the new justice minister. David Ford, the leader of the non-sectarian Alliance party, is expected to hold the post for an interim period to reassure Unionists.
Emerging from the meeting at Stormont, as the clock in the Great Hall approached midnight, Robinson said: "We have a basis upon which we can go forward and recommend it [the deal] to our party, to the other parties in Northern Ireland and to the community. An essential element of the Democratic Unionist party's manifesto is the requirement for community confidence, we believe this can be the basis for gaining that confidence."
Gerry Adams, the Sinn Féin president, said: "I believe that the assembly and political institutions can now proceed on the basis of equality, fairness and partnership. They also have to deliver for all citizens, that is the collective responsibility of all the political parties."
Shaun Woodward, the Northern Ireland secretary, hailed the deal as the final part in the jigsaw of the peace process. Power-sharing between the DUP and Sinn Féin, launched in May 2007 in the final weeks of Tony Blair's premiership, had been unstable because the two sides were unable to agree on the final stage of devolution – handing powers on policing and criminal justice to the executive.
Sinn Féin insisted that handing over the powers was an essential part of the St Andrew's agreement of 2006 which paved the way for the May 2007 deal. The DUP insisted that such a major step could only be taken when Unionists had full confidence in the institutions.
The deal last night marks one of the most significant milestones in the Northern Ireland peace process. This dates back to April 1993 when John Hume, the former leader of the SDLP, took what was then the mammoth step of inviting Adams to his house in Derry for talks.
This sparked an intense process – involving London, Dublin and eventually the Ulster Unionist party – leading to the Good Friday agreement of 1998. But this was not stabilised – the former UUP leader served intermittently as first minister – until the deal between Sinn Féin and the DUP in 2007.
British government sources praised the DUP and Sinn Féin. "Peter Robinson has shown the most extraordinary leadership," one source said. The DUP leader only assumed the post of first minister this week after standing down last month after the disclosure of damaging details about his wife's financial affairs.
The source added: "Sinn Féin have been very patient."