Mr Ahern and others addressed concerns around Brexit at a conference at Dublin City University.
President Michael D Higgins warned about political parties in Europe trying to divide people over race religion and nationality. The EU’s founding principles were threatened by “increasing inequalities in income, wealth, power and opportunities”, stressed Mr Higgins.
Rising inequalities and a blind acceptance of growth in the bloc had consequences, he said: “As a consequence, economic and social cohesion has fractured, and political policies resiling to, and deploying, rhetoric once thought banished from the continent of Europe have begun to re-emerge.”
Mr Higgins said he did not share the optimism of politicians in Europe on the future of its institutions. He also agreed with recent remarks by French President Emmanuel Macron, saying: “We must recognise that the union cannot, as in the past, be reconstructed from above, but can only, if it is to survive in this new century, be renewed and rebuilt from below.”
The President reminded the DCU audience that the First World War should have taught us that peace does not rest on common markets or globalisation, having broken out at a time of free capital.
Mr Ahern outlined his concerns and said he thought the Government had not sealed a proper deal before Christmas for a frictionless border in the North.
That agreement between Brussels and London said that, in the absence of a solution for Brexit, there would be no barriers between the North and the South and therefore no hard border.
Taoiseach Leo Varadkar says this commitment is “rock solid and cast-iron”.
But Mr Ahern poured fresh doubts on the deal. “The question comes back all the time — how can they [Britain] get these things and be out of the single market and out of the customs union? It was a fudge,” he said.
He aid international media had described the deal as provisional. “The British are pumping that out. I think we are going to have to rerun all of that again. It’s one thing fudging a statement or communique, which I’ve done many times in Europe, but that now has to be put into a legal context. You cannot fudge a legal context.”
And he also had some criticisms on Britain’s Brexit secretary, saying: “David Davis is a very interesting character but I watched him yesterday ... I continue to have my doubts — does he understand this stuff?”
Meanwhile, speaking in Davos, Mr Varadkar hinted that Britain may get a bespoke trade agreement with the EU after Brexit.
In an interview with Bloomberg, Mr Varadkar said he hoped the ultimate free trade arrangement could resemble “Norway Plus”. Norway has virtually full access to the single market, but it must abide by all EU rules and pay into the EU budget.
British Labour MP Hilary Benn told the conference he did not think a second Brexit vote would alter the outcome.
Many people knew how they voted, the EU had a history of trying to change votes and it was unclear from polls whether a fresh vote would be different, the House of Commons Brexit committee chairman said.