Attorney General Geoffrey Cox and Stephen Barclay head to Brussels to lead Brexit backstop talks

Attorney General Geoffrey Cox Credit: Jonathan Brady/PA

Attorney General Geoffrey Cox and Brexit Secretary Stephen Barclay are to hold fresh talks in Brussels in an attempt to secure legally-binding changes to the Northern Ireland backstop.

Downing Street has said negotiations are at a "critical stage" as Theresa May presses for concessions from the EU that will persuade MPs to back her Brexit deal in next week's expected crunch Commons vote.

Conservative Brexiteers are demanding guarantees the UK cannot be tied indefinitely to EU rules through the backstop, intended to ensure there is no hard border on the island of Ireland in the absence of a future free trade agreement.

However, French president Emmanuel Macron signalled he would firmly resist any measure that might diminish the security and integrity of the EU's external border and internal market.

He also accused Brexiteers of lying about the consequences of leaving the EU and suggested Britain would end up being part of a reformed Europe in the future.

No 10 refused to be drawn on Monday on a report that Mr Cox had dropped attempts to secure either a time limit or a unilateral exit mechanism in the face of entrenched opposition from the EU.

However, Mr Cox poured cold water on the claims describing then as "misunderstood fag ends dressed up as facts".

"Some of it is accurate, much more of it isn’t and what is not is far more significant than what is," he wrote on Twitter.

"Complex and detailed negotiations cannot be conducted in public."

The prime minister's official spokesman said the negotiations were "definitely making progress" but that there "definitely remains more work to be done".

Meanwhile, the so-called "Cash Council" of pro-Brexit Tory MP lawyers – named after arch Euro-sceptic Sir Bill Cash – said they would make a judgment on whether to vote an agreement once they had seen the details.

Council member Michael Tomlinson said any document would have to meet the requirements of the Brady amendment, passed by the Commons in January, which called for "alternative arrangements" to replace the backstop.

"There are no documents for us to examine at this stage, but we look forward to seeing in due course what the Attorney has agreed, so that we may assess whether it meets the requirements of the Brady amendment, which commanded a majority in the House of Commons and calls for significant, legally-binding changes to the Withdrawal Agreement," Mr Tomlinson said following the first meeting of the group at Westminster on Monday.

"We support the prime minister in seeking treaty-level changes, but pre-judging or speculating at this stage won’t help the re-negotiating efforts.

"The council has asked to be given all of the relevant documents in good time to consider them properly, in order to form a judgment in advance of a vote. Our primary objective is a proper analysis."

Emmanuel Macron tore into Brexiteers on Monday. Credit: AP

Mr Macron tore into Brexiteers on Monday, saying "anger mongers, backed by fake news, promise anything and everything".

He said: "Who told the British people the truth about their post-Brexit future? Who spoke to them about losing access to the European market? Who mentioned the risks to peace in Ireland of restoring the former border? Nationalist retrenchment offers nothing."

Indicating he will stand firm on the backstop, he said: "Our borders also need to guarantee fair competition. What power in the world would accept continued trade with those who respect none of their rules? We cannot suffer in silence."