Fianna Fáil leader Micheál Martin has said the only credible means of addressing Northern Ireland's economic needs post-Brexit was for it to become a special economic zone.
In an address to the Killarney Economic Conference, which is organised in partnership with The Irish Times, Mr Martin claimed such a designation "would threaten no one's sovereignty".
He said it would enable a means of allowing free flow of trade north and south, and also east and west.
“It would not in any way undermine the internal market of the UK as it is a model used throughout the world by states seeking ways of developing regions.”
He said those who opposed such a status for the North had used arguments that were not unjustified.
“It is effectively an economic development zone which doesn’t undermine the status of Northern Ireland, and one which provides the basis for respecting the wishes of the majority in Northern Ireland.”
Mr Martin also warned against negotiators rushing to microphones, which was received as an opaque criticism of comments made by Taoiseach Leo Varadkar and Tánaiste Simon Coveney in advance of the phase one negotiations concluded.
The DUP leader Arlene Foster also echoed those sentiments in her speech to the conference in Co Kerry.
Mr Martin also said he strongly disagreed with the view in some British quarters that the Brexit referendum result precluded criticism.
“I reject the idea that someone who challenges the chaos in Whitehall or points to Brexit damage can be dismissed as a ‘Remoaner’ or that no one has a right to complain because there was a referendum.
“This shows an intolerance towards the right of people to be true to their own beliefs and to point to hard facts.”
‘Squalid’ campaign
Mr Martin continued that while he respected the right of Brexit advocates to hold their view, he claimed the pro-Brexit campaign was “shabby and squalid”.
“It was largely based on fear-mongering and outright falsehoods. As the many insider accounts of the campaign have revealed in the last year – the overall Leave strategy was to say or do whatever was necessary and to hell with the facts and the consequences,” he said.
Mr Martin said there was a need for immediate and detailed discussions on how the different elements of the Good Friday Agreement are to be protected.
“For example, the text of the agreement and its enabling legislation explicitly requires the Assembly and Executive to operate in accordance with EU law. Prime minister May has said the agreement remains in place, so how exactly is this requirement to be addressed post-Brexit?” he asked.
“We need to know exactly how the complex balance of rights and obligations set out in the agreement will be vindicated when the enabling force of EU membership is removed.”
One of the impacts of the Good Friday Agreement was that all 1.8 million citizens of Northern Ireland were entitled to be EU citizens, even in the wake of Brexit, he pointed out.
“And I think it’s important that we put to rest the idea that politicians in the Republic advocating a deal which respects the rights and opinions of Northern Ireland is a constitutional threat. It’s actually the exact opposite.
“It is a vindication of long-established policy which underpins the core concept that the people of Northern Ireland alone will decide on its constitutional status.”
He also stood over the aspirations of Irish nationalism. “We have a right to express our aspiration for a single state for all on this island without this being presented as a threat to anyone.
“And I think through my words and actions I have more than earned the right to speak on this topic without being accused of following the agenda of Sinn Féin – which is in fact this island’s most entrenched anti-EU party.
“I have also been very clear in calling on Sinn Féin to allow the Northern institutions to get working. Only this will enable the anti-Brexit majority to have a place at the table during critical negotiations in the next nine months,” he said.
