Former Taoiseach and Fine Gael leader John Bruton has described as "gravely serious" any move by Britain to override the Northern Ireland Protocol.
Speaking to Morning Ireland, on RTÉ Radio 1, Mr Bruton warned that any such development would set a "dreadful precedent" in international relations.
"Remember we are at war. There is a war taking place in Ukraine because Russia is breaking a treaty guaranteeing the territorial integrity of Ukraine. And Britain is supporting Ukraine in that.
"And yet at the very same time they are proposing to break a treaty concerning their nearest neighbour Ireland and the European Union which they freely negotiated and indeed which was endorsed in the Conservative party manifesto of 2019 where it was described as a 'great new deal.'
Boris Johnson said there would be no more renegotiation
"Boris Johnson said there would be no more renegotiation. Now he wants to not just renegotiate it. He wants to break it."
Mr Bruton indicated that the EU cannot ignore what is happening in the UK parliament because the proposals being made on the Protocol would destroy the Single Market.
He said certain elements in the UK Parliament also want Northern Ireland to have access to the EU Single Market without any EU rules on state aid.
"They (also) want no jurisdiction for the European Court of Justice in interpreting EU rules as applied in Northern Ireland. That would mean the uniformity of the Single Market as far as rules are concerned is essential to it would be diluted. You would have one set of EU rules for Northern Ireland and another set of EU rules for the 27 member States."
Mr Bruton described the issues at stake as being "quite serious".
"If for example you had pathogens introduced in food in to Northern Ireland and not checked at the ports in Northern Ireland and some of those foods were incorporated in Irish exports you could have a major food scandal damaging the Irish food industry potentially terminally as a result of lack of controls.
'Deeply destructive'
"These are deeply destructive proposals that the British are making, and they know perfectly well what they are doing. This is not something that was sprung on them. "
Meanwhile, DUP Leader Jeffrey Donaldson told the House of Lords yesterday that he feels like a second class citizen arising out of the Protocol proposals. He spoke about those who are trying to create an all island economy - an economy which he says does not exist.
Mr Bruton said there was "no validity" in the comments made by Mr Donaldson.
"Northern Ireland remains fully part of the United Kingdom for purposes of sovereignty, for purposes of military , for purposes of the service industry. All the Protocol is dealing with is a very small part of the economy which is the goods economy.
"In modern times services are far more important than goods. Because we have a land border, and with Jeffrey Donaldson's support Northern Ireland is leaving the European Union, we have to find some way of managing to ensure that what happens in Northern Ireland doesn't damage the single market of the European Union which is of vital national interest for us.
"But also to do the best we can to give businesses that are on this island of Ireland but in Northern Ireland privilege to access the EU market."
Mr Bruton said the Protocol would encourage investment in Northern Ireland rather than in the mainland of Britain.
"As it will have access to the EU market as well as to the UK market. That is a massive advantage for Jeffrey Donaldson's constituents. It could be argued that it solidifies the Union rather than the opposite. But Jeffrey Donaldson seems to me not to understand the economic interests of his constituents and is putting a purely abstract constitutional point in place of practical reality."
Mr Bruton added that the Belfast Agreement brokered 24 years ago has "never completely worked".
"The east/west dimension was almost completely ignored. The north/south dimension, which was quite ambitious in the framework document which John Major and I negotiated, was diluted down to very little in the final Good Friday Agreement.
"Power-sharing has worked only intermittently. We don't I think in Northern Ireland have collective responsibility. We have individual Ministers doing individual things. The Good Friday Agreement needs to be refurbished to work as a practical operation rather than something symbolic. The UK has done very little as the sovereign power to make it work properly."
