Britain's relationship with the EU has been plunged into crisis after ministers rejected a demand by Brussels to drop plans to override key elements of the Brexit Withdrawal Agreement.

At a stormy meeting in London, European Commission vice president Maros Sefcovic gave the UK until the end of the month to drop the controversial provisions in the Internal Market Bill or face the potential collapse of talks on a free trade agreement.

However, British Cabinet Office Minister Michael Gove - who co-chairs a joint committee on the Withdrawal Agreement with Mr Sefcovic - said the government was not prepared to back down.

"I explained to vice president Sefcovic that we could not and would not do that," he told reporters following the meeting.

"I made it perfectly clear to vice president Sefcovic that we would not be withdrawing this legislation. He understood that. Of course he regretted it."

EU chief negotiator Michel Barnier warned that "significant differences remain" in trade talks with the UK but said Europe is committed to a deal, despite a major row over their Brexit divorce.

After talks in London, he warned in a statement that "nobody should underestimate the practical, economic and social consequences of a 'no deal' scenario".

Lord Frost, the UK's chief Brexit negotiator, said: "These were useful exchanges. However, a number of challenging areas remain and the divergences on some are still significant.

"We have engaged in discussions in all areas. We have consistently made proposals which provide for open and fair competition, on the basis of high standards, in a way which is appropriate to a modern free trade agreement between sovereign and autonomous equals. 

"We remain committed to working hard to reach agreement by the middle of October, as the Prime Minister set out earlier this week.

"We have agreed to meet again, as planned, in Brussels next week to continue discussions."

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Earlier, Mr Sefcovic said in a statement that violating the Withdrawal Agreement would break international law and jeopardise trade deal talks.

He told Mr Gove "in no uncertain terms" that the "timely and full implementation" of the divorce deal is "a legal obligation".

"Violating the terms of the Withdrawal Agreement would break international law, undermine trust and put at risk the ongoing future relationship negotiations," the statement said.

The EU did not "accept the argument" that the UK Internal Market Bill was needed to protect the Good Friday Agreement.

"In fact, it is of the view that it does the opposite," the statement said.

"Vice-president Maros Sefcovic called on the UK Government to withdraw these measures from the draft Bill in the shortest time possible and in any case by the end of the month.

"He stated that by putting forward this Bill, the UK has seriously damaged trust between the EU and the UK. It is now up to the UK Government to re-establish that trust."

According to draft EU legal advice seen by RTÉ News earlier today, the European Commission would be allowed to take legal action on several grounds if the UK decided to override elements of the Northern Ireland Protocol in the Brexit Withdrawal Agreement.

The advice, which has been circulated to member states, says that the Withdrawal Agreement was ratified by both the EU and UK and entered into force on 1 February.

"Since then, no party can unilaterally change, clarify, amend, interpret or disapply it anymore," the advice says.

The Internal Market Bill will see the UK government reserve the right to unilaterally interpret the protocol's rules on state aid and customs declarations.

The EU’s legal advice says the Northern Ireland Protocol "forms an integral part of the Withdrawal Agreement... If adopted as proposed, this bill will be in clear breach of substantive provisions of the Protocol…"

Britain's Attorney General Suella Braverman publishe d the UK government's legal advice on the new legislation today.

Shadow attorney general, the Labour Party's Charlie Falconer, said: "The Attorney General offers no justification whatsoever for the UK acting in breach of the Northern Ireland Protocol and there is no justification for breaking the terms of that agreement.

"This advice does not address the issue of a breach of international law. The Attorney General has conspicuously failed in her duty to uphold the rule of law in this country."

While the legislation proposed only gives the UK government the option of taking unilateral measures that are contrary to the protocol, the legal advice to member states is that even by proposing the bill, the UK is in breach of the good faith element of the treaty, Article 5, "because this bill jeopardises the attainment of the objectives of the agreement".