The Belfast Agreement may have to be amended because of Brexit, the former British prime minister Tony Blair said on Friday.

Speaking to members of the European People’s Party in Druids Glen, Co Wicklow, Mr Blair said the Belfast Agreement was “formulated on the assumption that both countries were part of the EU”.

“This was not only for economic but also for political reasons, to take account particularly of nationalist aspirations. Some of the language will therefore require amendment because of Brexit.”

However, he said that “with goodwill, including from our European partners, this should be achievable with the minimum of difficulty”.

Asked about the prospect of a united Ireland, Mr Blair said, “I think you can see there’s going to be a big debate, as you’d expect, and there’s lots of people talking about it. But, in the end, it will depend on what the terms of Brexit really are.”

Mr Blair warned that “a hard border between the countries would be a disaster and I am sure everyone will and must do all they can to avoid it”.

“If the UK and the Republic were able to agree a way forward on the border, then we would have the best chance of limiting the damage. It is in the interests of us all, including our European partners, for this to happen,” he said, according to excerpts from his speech release by his office. The media was not permitted to attend the conference session with Mr Blair.

According to a person who was present, Mr Blair said the weak leadership of the British Labour Party by Jeremy Corbyn had facilitated Brexit, by having nobody to put a strong counter argument.

He said Britain was only now waking up to the realities of Brexit, and there remained a wide range of possibilities for the eventual deal.

He likened membership of the single market to playing in the Champions League, whereas a free trade agreement with the EU would be like being confined to playing in the Premier League.

Later, speaking to journalists, Mr Blair expressed his concerns for the future of the Belfast Agreement.

“As one of the architects of the Good Friday Agreement, which brought into being the peace process in Northern Ireland, I’m extremely anxious to ensure that Brexit does not impair that agreement,” he said.

Mr Blair said it was “vital to maintain” the common travel area.

And he said it was “important to safeguard as much as possible” the present arrangements.

Mr Blair said that “whatever disagreements I have with the British Government more generally over Brexit, there is a real consensus across the British political system that we must do everything we possibly can to keep the present situation between the Republic of Ireland and Northern Ireland as similar to what we have at the moment as we possibly can, and do all we can to minimise any potential disruption.

He said any changes to the Belfast Agreement should be “changes of language, not changes of substance”.

“The best thing is to treat northern Ireland as a special case, to treat this border as a special case, to make sure we keep the common travel area so people can move across the border freely.

“The biggest challenge is going to be really a challenge for the European Union because, after Brexit, the border becomes the border between the UK and the European Union,” Mr Blair said. “If there’s goodwill and a lot of ingenuity and innovation and maybe the use of technology and other things, I think we can minimise disruption. But obviously I’m worried, I warned about this during the referendum campaign.”

Meanwhile, the leader of the European People’s Party Manfred Weber said that Europe should be willing to change its laws and regulations to facilitate special Brexit arrangements for Ireland.

“Yes, if it’s part of a package of solutions, of course, no problem,” Mr Weber said when asked if the EPP and the European Parliament would co-operate in changing EU rules to facilitate a special deal to maintain a soft border in Ireland.

The EU’s negotiating guidelines promise to preserve the Common Travel Area between Ireland and the UK as long as it is in accordance with EU laws.

However, Mr Weber, leader of the largest group in the European Parliament, adopted a tough tone on the Brexit negotiations, saying that “in London there is too little awareness of what Brexit means”.

“They cannot take the bits that they like and not take the bits that they do not like. There will be no cherry-picking. Maybe they do not realise this,” he said. “If we allow cherrypicking people in the EU would see that leaving the EU is not a problem.”

Several EPP figures echoed his sentiments during the two-day meeting in Co Wicklow.

“In London there is too little awareness of what Brexit means,” Mr Weber said. “My perception is that London knows what they don’t want, but they have no idea what they actually want.”

He said that in Brussels “there is a readiness to be very tough. London must be aware of this.”

If there is no agreement between the EU and the British, Mr Weber said: “For us, damage. But for Great Britain, a disaster.”