The idea is splashed across British tabloid headlines. The London commentariat takes it as a given. Hard-line advocates of the divorce from the European Union say it would be a catastrophic mistake — but even they seem to expect it will happen.

The only problem? The remaining 27 E.U. nations are not sure they are willing to give Britain a break, according to diplomats involved in the discussions — and any reprieve requires their unanimous approval.

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The misalignment in views means that the risk of an accidental and chaotic no-deal Brexit on March 29 is increasing, according to diplomats and analysts in Brussels. (Most analysts in London, who have faith some solution can be worked out, don’t think there’s a problem.)

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The British assumption that Brexit could easily be postponed would extend the stream of false assumptions, misperceptions and miscalculations that have plagued London policymakers since the June 2016 vote to leave the European Union. But a no-deal departure that British policymakers do not desire would be the ultimate exclamation point to end the process. If Britain left without a transition plan in place, trade would screech to a halt. Food and medicine could become scarce commodities.

“I don’t see how the current deal can be tweaked,” Dutch Prime Minister Mark Rutte told reporters Friday, warning Dutch businesses to begin “urgent” preparations for a chaotic British departure.

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On Wednesday, Rutte said Brussels would look “charitably” on a Brexit extension request from London, echoing remarks from French President Emmanuel Macron and German Chancellor Angela Merkel.

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But there were strings attached — many of which seem to have sunk in the English Channel on their way over to Britain.

“We have to have an idea how they want to solve things, because it is no use to continue to run in circles for a few more months,” Rutte said.

That viewpoint is widely shared in Brussels: a willingness to entertain a British request for more time, but only on the condition that Downing Street gives credible assurances that it will not use the time to press for concessions that have already failed on the continent.

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Many policymakers working on Brexit in Brussels say Britain has given them little reason to expect a real plan.

“Miscalculations are a continuous fact,” one senior European diplomat said, speaking on condition of anonymity to offer a frank assessment of the British position. “There will be no extension with unknown purpose.”

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E.U. policymakers say they could foresee various scenarios that would warrant granting an extension. One might be if British Prime Minister Theresa May reconsiders her refusal to join the E.U. customs union, for example, which would take away Britain’s ability to do many trade deals but would simplify efforts to preserve peace in Northern Ireland by keeping the border with Ireland open. That has been a key sticking point in the negotiations.

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Or British leaders could commit to holding another Brexit referendum, opening the door to a total reversal. Or they could try to convince Europe that they were close to finding a compromise inside their own ranks and that they just needed a little extra time, policymakers and analysts said.

Still, to read the British press, Brussels is sitting and waiting to be asked.

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“E.U. ready to delay withdrawal until next year,” read one headline this week in the Times of London.

“Either those sources are uninformed or making themselves interesting or just speculating,” said the senior European diplomat.

“Take ‘no deal’ off the table now, please, prime minister,” Labour Party leader Jeremy Corbyn said in a speech Thursday. In recent weeks, he has demanded an extension of the Brexit deadline to give time to hold a new election, ignoring that Britain can’t change the deadline unilaterally.

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May, too, has an interest in keeping the March deadline as a way to force her own squabbling Tory camp to cooperate with her — and perhaps agree to the withdrawal deal they recently torpedoed. She has said, accurately, that she does not have the power on her own to delay Brexit.

The E.U.’s highest court ruled last month that Britain could unilaterally revoke Article 50, which initiated the withdrawal process, and reverse its decision to leave. But that decision does not apply to merely extending Article 50 and postponing the departure, which would need the okay of 27 other leaders.

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If there were to be an extension, it would be relatively easy to give one until late June, policymakers said. After that, giving Britain extra time becomes thorny, since Europe is holding elections in May for a new European Parliament that will be seated in July.

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“What we will not let happen, deal or no deal, is that the mess in British politics is again imported into European politics,” tweeted Guy Verhofstadt, Brexit coordinator for the European Parliament. “While we understand the UK could need more time, for us it is unthinkable that article 50 is prolonged beyond the European Elections.”

Letting a country remain in the European Union without parliamentary representation is legally questionable, since European treaties require it, and some European leaders fear a challenge from U.K. citizens or others if they allow it to go forward.

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Allowing Britain temporary representation inside the European Parliament is also politically unpalatable, since many in the current British delegation are the euroskeptics who advocated Brexit in the first place.

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Analysts said that there may also be a cultural split at play in the clash of expectations. Britain’s legal system tends to give flexibility to policymakers because less is enumerated in black-and-white legal codices. Not so in continental Europe, where legal systems are usually based on unbending Napoleonic code.

“In a system without a constitution, everything is possible until the very end,” said Fabian Zuleeg, the chief of the European Policy Center, a Brussels think tank.

That creates a risk of a miscalculation. And because there appears to be no majority in the British Parliament for any given Brexit plan, the default course — a chaotic crash-out in March — may be the likeliest path, he said.

“No deal is the default,” he said. “It is the only option on the table where you don’t need a majority.”