The European Union's Finnish Presidency demanded on Thursday that Britain deliver a new written Brexit proposal by the end of September or face a messy "no-deal" divorce, an ultimatum immediately rejected by London. Britain is racing toward its October 31 departure without an exit agreement and facing the threat of border disruptions that the government admits could cause food shortages and spark civil unrest. The sides have been irreconcilably split over ways to avoid a hard border between EU member Ireland and the UK's Northern Ireland in any Brexit scenario.

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Demand for a new proposal

An agreement that includes the so-called "backstop", which would temporarily keep Britain in the bloc's customs union, has been repeatedly rejected by the UK parliament. Prime Minister Boris Johnson has vowed to come up with a new solution and not to sign any in which the backstop remains. But EU officials have rejected London's past suggestions and have called for a clear alternative well before Johnson attends a potentially decisive EU summit in Brussels on October 17-18. A spokesman for the Finnish Prime Minister Antti Rinne said

"The UK must come up with a written proposal by the end of this month". Finland holds the EU's rotating presidency and occasionally speaks for the bloc.

But a Downing Street spokesman said London would spell out its views when it was ready and when Brussels adopted a more constructive tone. "We will table formal written solutions when we are ready, not according to an artificial deadline, and when the EU is clear that it will engage constructively on them," the UK government spokesman said.

Brexit: Finnish PM Says UK Has 12 Days To Give A Written Proposal

The latest salvo in the ongoing war of words between London and Brussels was fired despite reports of feverish negotiations being held in various European capitals. European Commission chief Jean-Claude Juncker told Britain's Sky News television that the EU was open to dropping the backstop if Johnson's government came up with a fail-safe alternative. "If the objectives are met, all of them then we don't need the backstop," Juncker said. "If the results are there, I don't care about the instrument." The British government spokesman said London has submitted "a series of confidential technical non-papers" with its thoughts on the dispute. Technical "non-papers" are documents used in negotiations that do not represent a formal position. But EU Commission spokeswoman Mina Andreeva refused to call the papers an official written proposal.

"There are papers for now, until we have looked at them in detail, I will not characterise them beyond being papers," she told reporters in Brussels.

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Juncker said Brussels had received them late Wednesday and that he had not had a chance to read them through. The UK papers are likely to be on the agenda when UK Brexit Minister Stephen Barclay meets the EU's chief negotiator Michel Barnier in Brussels on Friday.

"The prime minister returned from talks with President Juncker in Luxembourg on Monday with assurances that negotiations will intensify," Barclay said on a visit to Madrid.

Brexit: Michel Barnier Does Not Want Pretense On Negotiations

Brexit agenda in UN General Assembly

A European source said the Brexit timetable will also be discussed at a meeting between Johnson and Juncker on the margins of the UN General Assembly in New York next week. Johnson may be given yet another headache when the UK Supreme Court rules next week on whether his contentious five-week suspension of parliament was unlawful. We "know that this case must be resolved as quickly as possible and we hope to be able to publish our decision early next week," Supreme Court President Brenda Hale said. A decision against Johnson could complicate his attempts to ram any deal that he does clinch with Brussels through parliament once its returns on October 14.

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