The final days of an intensive campaign have seen a decisive shift towards the "Yes" camp, leading to estimates of a pro-agreement vote ranging from 65 to 72 per cent.
Any figure close to 70 per cent will come as an intense relief to the Government and the pro-agreement parties, since it would represent a significant recovery after a near-disastrous start to their campaign.
Last night the signs were that intensive campaigning by the Ulster Unionist leader, David Trimble, and in particular by Tony Blair, had first staunched a flow of Unionists to the "No" camp and then, in the final days, turned the tide. Both the Prime Minister and the Ulster Unionist party said they detected a late surge among the large number of undecided Unionists into the "Yes" camp.
The "No" camp yesterday staged a line-up of leading figures including the Rev Ian Paisley, leaders of the Orange Order and important MPs from Mr Trimble's party. The final images generated by the pro-agreement campaigners were those of Mr Blair signing a hand-written list of pledges to Unionists, and of Mr Blair posing between Mr Trimble and the SDLP leader, John Hume.
Those on both sides of the argument spent a whirlwind final day seeking to sway those Unionists who, after six weeks of debate, said they were still undecided on how to vote today. There were a number of bad-tempered moments, as hecklers shouted at the Prime Minister, Mr Trimble and the Unionist "No" campaigner Robert McCartney.
All the activity was concentrated on the Unionist side, since, according to the opinion polls, support for the agreement among northern nationalists has reached an extraordinary 96 per cent. The pro-agreement vote in the Republic, which holds its own simultaneous referendum today, is also expected to be overwhelming.
Mr Blair, who was again in the forefront in campaigning for a "Yes" vote, was heckled while visiting a Belfast hospital by one man who shouted: "You're a rebel, Blair, go back to England where you belong, you're not wanted here."
But the Prime Minister was also cheered on the same visit, receiving generally supportive messages as he carried out a morning of engagements. In an upbeat assessment he said: "My sense is that we are moving towards a `Yes'. Last week people were concerned, but this week they are re-focusing on the big picture, and seeing as a whole the agreement is right. People here have a very strongly developed sense of justice, of moral justice, and people understand this agreement is a just agreement."
Mr Paisley later responded: "Mr Blair's assurances, handwritten or not, are worthless and the people will not be taken in by these assurances. The people of Northern Ireland are not going to believe the Prime Minister."
Mr Blair in turn rejected the "No" camp's contention that only a 74 per cent "Yes" vote would be decisive. He said: "That's simply not correct. I want as many people to support us as we possibly can. That's because I believe this agreement is right and it's just."
Two potentially important voices meanwhile endorsed the "Yes" campaign. The Church of Ireland Archbishop of Armagh, Dr Robin Eames, said he had agonised over almost every page of the document before arriving at his decision.
He added: "I have big problems with this document, but none of us want the grandchildren of Northern Ireland, let alone the children of Northern Ireland, to live their lives as so many of us have had to live ours."
A further endorsement came from Sir John Hermon, former chief constable of the Royal Ulster Constabulary, whose stance may influence members of the force who had yet to decide how to vote. Appearing alongside Mr Trimble, he said: "A `Yes' vote will hold the centre ground of moderation and leave the extremists where they ought to be - out on the extremes." The Tory leader, William Hague, who was also in Belfast, urged people not to be complacent and to turn out at the polling stations, saying that a small majority in the poll would be "very dangerous".