The Prime Minister yesterday sat down across the Cabinet table from the former chief of staff of the IRA and told him: "May I look you in the eye and hear you say you are committed to peaceful means?"
Six years earlier, John Major's Cabinet had dived for cover under the table during an IRA mortar attack. The risks of the meeting were not lost on Mr Blair and Mr Adams, nor was the sense of history. After walking through the front door of Downing Street, the Sinn Fein delegation waited in an ante-room decorated with portraits of past prime ministers, Lloyd George, Balfour and Gladstone, all of whom, Mr Adams reminded Mr Blair in the talks, had tried and failed to resolve the Irish question.
Michael Collins, the last Sinn Fein leader to have crossed the threshold of Number 10, in 1921, was assassinated a year after signing a deal with Lloyd George which led to partition, which Mr Adams said was "unfinished business".
Mr Adams, Martin McGuinness, and five Sinn Fein members arrived 10 minutes early for their meeting, to be greeted by cheers from supporters and jeers from opponents. As Mr Adams and Mr McGuinness stepped inside, they were handed a Christmas card bearing a dove of peace by Rita Restorick, mother of the last soldier killed in Northern Ireland.
There was a handshake between Mr Blair and Mr Adamsbefore the Prime Minister showed Mr Adams, Mr McGuinness and their delegation to the Cabinet room, where they used first names over cups of tea. Mr Blair was flanked by officials and Mo Mowlam, the Northern Ireland Secretary, who pointed out that it was "not helpful" for the Sinn Fein leader to have wished "good luck" to the IRA killer who escaped from the Maze Prison on the eve of the talks.
Across the table, they faced a delegation which included some with criminal records for terrorist offences. There was a symbolic importance in the meeting, Mr Blair told the Sinn Fein leaders, but it was more important that they were working for a settlement. If there was a return to violence they "would lose the best prospect we have had for a generation and there can be no going back to that."
Mr Adams had responded to the Prime Minister's challenge by saying Sinn Fein had signed up to the six Mitchell principles, which included a commitment to "democratic and exclusively peaceful means of resolving political issues", to gain entry to the cross-party talks.
Later Mr Blair defended the meeting: "What I think is worth doing is taking risks, even with people who in prior times have been engaged in activity we have all condemned. It's important to take those risks to give us that chance. I know it's difficult for people when they see Sinn Fein coming into Number 10 Downing Street."
Mr Adams said: "We come from a small island of 5 million people of grief and pain and division over the centuries. We want to see it ending ... This was a good moment in history."
The Sinn Fein team raised a shopping-list of causes - demands for a public inquiry into Bloody Sunday; release of republican prisoners; removal of high-tech observation posts in Armagh; abolition of Britain's legislative claim to sovereignty over Ulster. A member of the team said decommissioning was never mentioned. After yesterday's talks, which both sides described as "positive", the peace process remains on track.
Mr Adams urged Mr Blair to press David Trimble, the Ulster Unionist leader, to agree to a face-to-face meeting with the Sinn Fein president. Downing Street conceded that was one request outside Mr Blair's power.