Mr Coveney was responding to a Financial Times report that said British legislation out this week will “eliminate the legal force of parts of the withdrawal agreement” in areas including state aid and the new customs arrangements for Northern Ireland.

In a statement, the UK government said it was working with the European Union to resolve what it called “outstanding issues” surrounding the Northern Ireland Protocol.

Without making explicit reference to the Financial Times report or specifying what the outstanding issues were, the statement stated that if those issues were not resolved “as a responsible government, we are considering fall back options in the event this is not achieved to ensure the communities of Northern Ireland are protected”.

Senior government sources would not be drawn on the Financial Times report, with one source speculating that it was part of a stepping up of “noise” by the UK as the future relationship negotiations enter a critical phase.

The source said he expected that the European Commission Brexit Task Force would seek clarification on the report.

Quoting three Whitehall sources, the report claims that sections of the upcoming Internal Market Bill would undercut key provisions of the Northern Ireland Protocol.

These included the potential levelling of tariffs on goods moving from Great Britain to Northern Ireland after the Brexit transition period ends on 31 December, as well as the potential for EU state aid law to continue to reach into the UK if the British government subsidises companies that have significant subsidiaries in Northern Ireland.

The report claims that “clauses in the internal market and finance bills will force the UK courts to follow the new UK law rather than the EU deal, diluting the ability of the protocol to intrude on UK state aid policy.”

The paper quoted one source as saying that the force of the new legislation had been approved by the UK’s chief negotiator, David Frost, who “had personally driven the decision to take the ‘nuclear option’ of overwriting the withdrawal agreement, despite progress being made in talks on implementing the Irish protocol”.

Reaction to the report has been swift, with Mr Coveney issuing his response on Twitter, saying: “This would be a very unwise way to proceed.”

The EU’s chief negotiator Michel Barnier said the Brexit terms that Britain agreed to before formally exiting the European Union “must be respected”.

“Everything that has been signed must be respected,” Mr Barnier told France Inter radio, in response to the Financial Times report.

Northern Ireland Deputy First Minister Michelle O’Neill said on social media: “As the Brexit negotiations between the EU and British government enter their eighth round this week in London, any threats of a roll back on the Irish protocol would represent a treacherous betrayal which would inflict irreversible harm on the all-Ireland economy, and [Good Friday Agreement].”

SDLP leader Colum Eastwood said: “If true, this could lead to a hard border in Ireland and undermine decades of progress.

Britain’s Agriculture and Environment minister George Eustace denied the UK government intends undermining the Withdrawal Agreement and Northern Ireland protocol.

He said the British government is committed to implementing the Withdrawal Agreement and the UK is working with the EU through the Special Committee established by the Agreement to jointly agree the specific terms of the treaty.

He said when that process ends there may be some outstanding issues – what he called “loose ends” that may need to be implemented through UK legislation.

Mr Eustace said these included the exact nature of checks required on food products entering Northern Ireland, and the type of exit declarations needed to document the movement of goods from Northern Ireland to Great Britain.

The report coincided with a combative statement from the British Prime Minister, which said that if there was no agreement between the EU and UK before an EU summit on 15 October then a free trade deal was unlikely “and we should both accept that and move on”.

Boris Johnson added: “We will then have a trading arrangement with the EU like Australia’s. 

“I want to be absolutely clear that, as we have said right from the start, that would be a good outcome for the UK. As a government we are preparing, at our borders and at our ports, to be ready for it.

“We will have full control over our laws, our rules, and our fishing waters. We will have the freedom to do trade deals with every country in the world.

“And we will prosper mightily as a result.”

What British ministers sometimes refer to as an “Australian” style free trade arrangement is generally taken as a “no deal” outcome, with both the EU and UK trading on WTO terms.

Mr Johnson said: “Even at this late stage, if the EU are ready to rethink their current positions and agree this I will be delighted.

“But we cannot and will not compromise on the fundamentals of what it means to be an independent country to get it.”

The EU-UK future relationship negotiations have been deadlocked for months over fisheries, the issue of state aid and the so-called level playing field, police and judicial cooperation, and how both sides would resolve disputes in the future.

The prime minister made no reference to the Northern Ireland Protocol in his statement.

Both teams of negotiators meet in London on Tuesday for the next full round of negotiations.

Mr Barnier has set a deadline for agreement of 31 October.

With many thanks to: RTE News and  Tony Connelly Europe Editor for the original story