Bertie Ahern has pleaded with both Dublin and London in the Brexit negotiations to “cool it”.
Speaking to Sky News, the former Irish prime minister also accused Boris Johnson and Liam Fox of sending confusing messages on the Irish border.
And, he said, the International Trade Secretary has shown a worrying lack of knowledge and a misunderstanding of what the border means to Ireland for the past 100 years.
He said: “Theresa May… has been fairly consistent, but Boris was over here last Friday and he gave a different message. We got a different message (from Liam Fox) yesterday.
“So it is confusing. And if you take yesterday’s message, which was… we’re not going to make any deal on this until we know the full extent of trade; for somebody to say that is such a misunderstanding, or a lack of knowledge, of what the border means the last 100 years. It’s worrying.
“It doesn’t help the position here when you have two senior ministers, contradicting things in the space of nine days. That’s not helpful.
“The Brexit vote, unfortunately, and I said it and knew it from day one, that this was going to dig up enmities and animosities of the past and we need to try and cut that out because it’s in nobody’s interest.
“We’ve good relationships and we work well together. We should not be unwinding that. I know what the British press has been saying in the last few days and my simple message from a guy that was involved in the Good Friday agreement is ‘I think we should all cool it’.”
Mr Ahern also deviated from the position of the Irish government suggesting that technology should be used to overcome customs checks.
It comes as Ireland’s foreign minister Simon Coveney stressed that all EU27 leaders agree that trade talks cannot start unless Britain offers further assurances there will be no hard border with Northern Ireland.
Michel Barnier has also claimed the “moment of truth” in Brexit negotiations is approaching and the European Union hopes for agreement on so-called withdrawal issues “in the next few days”.
The EU’s chief negotiator called for “real, sufficient progress” on the Brexit “divorce bill”, citizens’ rights and the Irish border, so that EU leaders can green-light talks on trade and a transition period before Christmas.
Prime Minister Theresa May has been given until 4 December to come up with further proposals on the withdrawal issues so Mr Barnier can recommend to leaders at the 14/15 December European Council summit that enough progress has been made for trade talks to begin.
At an EU summit in Tallinn, Estonia, Mr Barnier said: “We need to have real, sufficient progress in the three key areas where the UK’s decision has created a lot of uncertainty and fear even.”
Amid fears there could be a return to a hard border in Ireland given the UK Government’s commitment to leaving the European single market and customs union, which allow for frictionless trade, he said: “We don’t want to be putting up barriers again and we need furthermore to maintain the integrity of the single market.”