BRITAIN and Ireland reached agreement last night on the decommissioning of IRA weapons to break the deadlock in Northern Ireland .
Details of the initiative will be outlined in the Commons tomorrow by Mr Blair, who stressed that it still had to be agreed by Ulster's political parties.
The deal was thrashed out in three weeks of talks between British and Irish officials and finally agreed at an unscheduled 20-minute meeting between Mr Blair and John Bruton, the outgoing Irish Prime Minister, at the United Nations Earth Summit in New York.
Although British officials tried to play down suggestions of a breakthrough, Mr Bruton said he believed there was now a prospect of "rapid forward movement" in Northern Ireland .
Both governments will insist on a commitment from Sinn Fein-IRA to the progressive surrender of weapons as the talks progress. Sinn Fein would be able to enter the talks after the restoration of a genuine ceasefire without the IRA first having to surrender some of its weapons.
Before leaving New York for London last night, Mr Blair said: "It is possibly the basis for a way forward but it has got to be agreed by the other parties. We want to try to move this process forward. But it cannot just be done by the British and Irish governments talking to each other. Other people have got to be involved too."
Mr Blair is expected to brief Ulster party leaders, including David Trimble of the Ulster Unionists and John Hume of the nationalist SDLP later today.
He will also seek an early meeting with William Hague, the new Tory leader, to outline the proposals and seek an assurance that the Tories will maintain a bi-partisan approach.
British officials accompanying the Prime Minister cautioned against expecting "dramatic" announcements in tomorrow's statement.
Mr Blair will outline the Government's latest thinking on decommissioning, the timetable for Sinn Fein's inclusion in talks following a resumed ceasefire and confidence-building measures.
They acknowledged that a joint approach had been agreed between the two governments based on the Mitchell principles.
Mr Blair is anxious to capitalise on what he believes is a changed mood towards the IRA since the murder of two RUC officers in Lurgan last week. Although he accepts the outrage was a great "setback" for efforts to bring Sinn Fein into the talks process, it has left the IRA increasingly isolated.
