The European Union gave Britain 48 hours to rework its Irish backstop proposal as part of the Brexit negotiations Wednesday — 22 days before the United Kingdom is due to leave the EU.

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With less than a month to go, the two sides are locked in a game of brinksmanship, and attempts to reach a mutually acceptable deal could go down to the wire.

EU diplomats, briefed on negotiations, said the U.K.'s top lawyer Geoffrey Cox had proposed a disputed arbitration panel that would not be obliged to refer cases to the European Court of Justice (ECJ), the EU's top court, whose jurisdiction Britain voted to leave in a damning 2016 referendum.

"We are now in a state when we are discussing proposals we have rejected months ago," an EU diplomat said. "They've sent in a criminal lawyer who doesn't know EU law or customs rules. We are explaining from scratch why his ideas won't fly."

British Prime Minister Theresa May had tasked attorney general Cox with securing concessions from the EU on a key demand of pro-Brexit lawmakers, namely that divorce provisions would not trap the U.K. in the bloc's trade rules, and would ensure that no hard border between Northern Ireland, part of the United Kingdom; and Ireland, an EU member state. EU negotiators objected that the Cox proposal would undo the Withdrawal Agreement reached by the EU and U.K. last year after months of tortuous negotiations.

Britain's parliament rejected that pact, largely over concerns over the backstop with Ireland. The EU bloc has offered addendums and extra assurances on the text to make it more palatable but refuses to change the substance of the pact.

Trying to secure changes to the so-called backstop — an insurance policy to prevent the return of border checks on the island of Ireland — ended Wednesday without agreement, with EU officials telling British negotiators to go back and redraft their proposals.

"They are simply not moving - they are not prepared to do what needs doing," the British source said. "It is always possible something might change in the next 48 hours but at the moment there is nothing to suggest that."

Many Labour Members of Parliament and some Conservatives back an even closer arrangement with the European Union - dubbed the "Common Market 2.0" plan - which would see the UK remain in the EU's single market by staying part of the European Economic Area. Jeremy Corbyn and the Labour leadership prefer that the U.K. remain in a customs union with the EU.

"I am reaching out to all groups in Parliament to try and prevent a no-deal Brexit which I think would be very damaging," he said. "We are looking at all the options."

While the EU still hopes for a breakthrough on the weekend, Brussels fears British Prime Minister Theresa May could try to negotiate directly with the other 27 EU leaders at a Brussels summit taking place March 21-22, just a week before the day Brexit takes effect.