Unionists do not care about the European Court of Justice’s oversight of post-Brexit arrangements in Northern Ireland, Dublin has claimed, prompting a furious backlash from Belfast and London. 

Simon Coveney, Ireland’s foreign affairs minister, said that none of the politicians or business people he had spoken to in the province had raised concerns about the oversight of the EU’s highest court. 

Intensifying his war of words with Lord Frost on Monday morning, Mr Coveney claimed that the issue of the ECJ was being used by the UK to sink any prospect of the two sides agreeing changes to the Northern Ireland Protocol. 

“I’ve spoken to many Unionists and I’ve spoken to many business people in Northern Ireland, and none of them are raising the issue of the ECJ jurisdiction in terms of the interpretation of the EU single market on the implementation of the protocol,” he told Ireland’s national broadcaster RTE.

His comments were swiftly rebuked by UK government sources, while senior DUP figures dismissed it as “complete nonsense” and warned that the role of the court was at the “heart of our objections to the protocol”.

The protocol, which was established to prevent a hard border on the island of Ireland, requires Northern Ireland to continue to follow the EU’s customs and single market rules. 

The consequence has been to erect a new trade barrier in the Irish Sea, causing significant disruption for goods destined for the province from the British mainland. 

The ECJ is the supreme interpreter of the rules of the single market, but the UK is now demanding that it no longer has oversight over a renegotiated agreement, which would also seek to drastically reduce the amount of red tape imposed on British goods.

In a bid to resolve the long-standing dispute, the EU intends to propose solutions this week which include allowing British sausages and chilled meats to continue to be sold in Northern Irish supermarkets. 

Maros Sefcovic, the Commission vice president, will unveil four proposals on Wednesday, covering the supply of medicines, animal health rules, customs procedures and a stronger role for Northern Ireland’s institutions in managing the protocol.

‘ECJ is a red line’

But Lord Frost will make clear that the ECJ is a “red line” for the UK in a keynote speech in Lisbon on Tuesday, warning that the EU has been “too quick to dismiss governance as a side issue”.

Instead of the EU’s top court in Luxembourg ruling on questions of European law in Northern Ireland, Lord Frost wants it replaced with an arbitration panel similar to the one agreed in the Brexit trade deal.

Ahead of the speech, Mr Coveney accused the British Government of “shifting the playing field” away from solving issues around the controversial protocol, adding that the protocol was underpinned by the ECJ’s oversight.

“The functioning of the EU Single Market relies on the European Court of Justice as the interpreter of the rules… the whole point of the protocol is that it extends the EU Single Market for goods to Northern Ireland to prevent the need for border infrastructure on the island of Ireland,” he continued.

“They are putting up this new red line issue, of jurisdiction of the ECJ. The truth is that they know the EU can’t move on this issue, yet they’re still asking for it.” 

Mr Coveney said that unionists in Northern Ireland were more concerned about trade barriers with Britain, adding: “The European Commission is trying to solve those issues as much as they can within the confines of the protocol.”

Hitting back at Mr Coveney, a gGovernment source said: “There definitely is a concern [about the European Court of Justice.] I think what’s more likely is there is no Unionist who actually wants to talk to Simon Coveney. 

“The case we are making is that it is really fundamental to the problems with the protocol. It’s clear that it is not the basis for a sustainable relationship.” 

Lord Dodds, the former deputy leader of the DUP, told The Telegraph: “This is nonsense from Simon Coveney. The DUP have always made clear there are two issues with this protocol: one is trade barriers and the second is the constitutional-legal position of Northern Ireland being in the EU jurisdiction for the EU Single Market and Customs Union. 

“It is exactly what we have been raising since the backstop was first proposed by Theresa May and later replaced by the protocol. 

“It is laws being made in Brussels, with no say of anyone in Northern Ireland, and then the application of those laws by a foreign jurisdiction. 

“Whether it’s the ECJ or the application of the laws through direct regulation, it is all about sovereignty. This is nothing new, this is not technical, this is at the heart of our objections to the protocol. 

“So Coveney is completely wrong in trying to make out that the ECJ is some tiny technical matter, what it speaks to is the entire issue of sovereignty.”