Good Friday Agreemnent: Bill Clinton discusses decision to grant US visa to Sinn Fein's Gerry Adams in 1994

Mr Clinton was speaking at Queen’s University Belfast at events marking the 25th anniversary of the Belfast / Good Friday Agreement.

He said: “He asked for a visa and we agreed so I could make the United States look like an impartial body, we would grant the visa for two days but there would be no fundraising.

“Everybody knew that a lot of money was going into Ireland from the north east United States, but not on this trip.

“We wanted to send a signal that we wanted to be involved but we wanted to be fair to everybody.”

He added: “At the time it was crazy they thought, but I thought it made all the sense in the world because what we were doing was not working and it seemed to me just from the talk that the public was maybe way ahead of the politicians in their desire to have some sort of resolution to this.

“So I gave Gerry the visa and he kept his word as he always did in dealing with me and the rest is history.”

Political leaders “winged it” in terms of the Northern Ireland peace process, he said.

Recalling those days at a panel event at the Queen’s University Belfast alongside former prime minister Tony Blair and former taoiseach Bertie Ahern, Mr Clinton said under the pressure at that time, “some of your decisions will be wrong or will be questioned or will not be good for one of your partners on any given day”.

“It just happens, nobody’s perfect, you can’t foresee all this, and the fact that we trusted each other and we trusted (George) Mitchell, I think we earned the trust of the parties in Northern Ireland that we were dealing with pretty across the board, because they thought we would be straight with them, and that’s how it happened,” he said.

“There were days I felt like I was taking Seamus Heaney’s advice to take a flying leap and walk on air against your better judgment. That’s how it started. We all just decided that the time was right to do the right thing.”

He said people thought they were crazy to believe they could get the paramilitary groups to decommission their arms.

“We’d like to tell you that we had it all thought through but the truth is we made up a lot of it as we went along, we had to wing it,” he said. “And then when (George) Mitchell came in, he organised our efforts.”

Mr Clinton has said he took an interest in the Northern Ireland situation when he first came to Oxford in 1968.

Mr Clinton told a conference in Belfast that when he was running for president, he made the decision to appoint a special envoy for Northern Ireland.

He said: “The State Department had operated for decades on the theory that our relationship with the UK was so important we couldn’t mess it up.

“Even President Kennedy, on his heralded visit to Ireland, did not go to the north and did not talk about it. This was one of those things that wasn’t done.

“I thought it was crazy to deny such a large problem’s existence and to take a pass when we had the biggest Irish diaspora.”

He added: “The British press was so bad that they were speculating that I just did it to burn John Major because he checked my passport files for the Bush campaign in 1992.”