Former Irish premier Bertie Ahern has said a border poll on a united Ireland would not have a “hope in hell” of passing at present.
Mr Ahern said “work has to be done” on how a united Ireland would work both economically and socially before a vote can be held.
He added that academic work was under way to examine how that could be achieved.
Mr Ahern made the remarks as he addressed an Irish parliamentary committee meeting in Dublin on his role as one of the architects of the Good Friday Agreement.
“There are a whole lot of questions,” the former Fianna Fail leader said.
“How would you bring together An Garda Síochána and the PSNI, how would you bring together the courts? How would you bring together local authorities? How would you bring together the National Health Service and the HSE.
“They’re all big questions. But they’re doable.”
But Mr Ahern cautioned without that work being completed prior to a poll: “I’ll tell you what the result of the election will be now and I won’t charge anything for the advice.
“It wouldn’t have a hope in hell of passing.”
He added that he thought people would see that it would be “illogical” to vote for a united Ireland without planning for one being completed.
Asked whether a Citizens’ Assembly might be a way of examining issues relating to a border poll, Mr Ahern said Citizens’ Assemblies had sorted out “thorny” issues in Ireland in recent years but he did not believe it was the best option available in this instance.
“To put the national question that we’ve been talking about for 100 years into the hands of 100 people. Well, I’m not too sure about that,” the former Taoiseach said.
“If I was one of the 100 I might have a different view. But I’m not sure I want to hand that over.
“I think it should be debated within political parties, within civil society.”
Mr Ahern also told the committee that progress on the Good Friday Agreement had been made due to the work of both the Irish Government and the UK Government.
“My observation of the evolution of the Northern Troubles from 1969 onwards was that it was only by the two Governments working hand in glove that progress could be made on Northern Ireland,” he said.
He added that while securing and implementing the Good Friday Agreement was not easy, it has made a huge difference.
“Today, almost 25 years later, we can look back on a generation of peace, a generation in which the guns have been largely silent, a generation in which a life unimaginable over the previous three decades has been possible for everybody in Northern Ireland,” he said.
“To paraphrase John Lennon, peace has been given a chance, and the results have been remarkable.”
