Sir John Major has acknowledged that IRA and republican leaders risked their own lives in the interests of forwarding the peace process.

The former prime minister told an audience in Dublin on Wednesday night that he was "acutely conscious" that IRA commanders were taking risks for peace.

In a speech marking the 20th anniversary of the Downing Street Declaration – an Anglo Irish governments communiqué that helped advance the peace process in 1993-94 – Major praised the work of former Irish premier Albert Reynolds in nudging the Provisional IRA towards its ceasefire.

"Let me now say something that may surprise you. Throughout the process, I was acutely conscious that IRA leaders were taking a risk, too: if Albert [Reynolds] and I upset our supporters we might – as Albert put it, be 'kicked out'. That was true but the IRA's supporters were more deadly than our backbench colleagues. And their leaders were taking a risk too, possibly with their own lives," the former PM said.

Later Major admitted to the Guardian that the British government had extensive intelligence around late 1993 that a so called "peace camp" within the IRA was gaining the upper hand within the Provisionals and moving towards a cessation of violence.

Major and Reynolds announced their joint declaration just weeks after one of the bloodiest periods of the Troubles that included the IRA bombing on Belfast's Shankill Road and the UDA massacre at a bar in Greysteel in Co Derry

During his visit to Dublin, Major also expressed concern that a possible exit from the UK would "unsettle the Catholic community" in Northern Ireland. Major said the nationalist community in Northern Ireland was strongly supportive of the Republic's pro-EU stance.

Defending the European Union and its founding principles, Major told a gathering that included Irish deputy prime minister Eamon Gilmore: "The EU can be irritating and frustrating: believe me, I know. But those in the UK who want us out have never articulated a viable alternative, let alone a better one.

"This is the black hole in their argument – because the truth is that the alternative would be bleak."

He said he could understand Irish fears about a possible UK exit from the EU and the impact that would have on its economy.

Major said he could "not believe that we would be so foolish" as to let Britain leave the EU.