Thanks to this precisely calibrated ecosystem and the European Union’s borderless trading zone, British shops can order fresh produce early in the morning and receive it by the end of the day.

But a no-deal Brexit threatens to throw it all into chaos, resulting in trucks backed up for miles, vegetables spoiled and economic pain for everyone.

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The Netherlands — Britain’s main trading partner on mainland Europe — is among the most prepared for the possibility that Britons will leave the E.U. on March 29 without a deal to manage the withdrawal. But leaders here fear that the best efforts of a nation that loves to be prepared may not be enough to safeguard against the mess. And Britain’s other trading partnerships in Europe could be even worse off.

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“Everyone is fully aware that something is going to happen,” said Mark Dijk, head of external relations at the Port of Rotterdam, whose docks, rail yards and warehouses handle nearly 1 million tons of goods moving to and from Britain every week. The port has been working on Brexit emergency plans for more than a year and is trying to alert businesses that they need to brace for a wave of restrictions.

Britain’s efforts to manage the withdrawal “are so chaotic that it’s hard for people to be sure there won’t be a [no-deal] Brexit,” Dijk said.

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No precedent exists for a country scissoring itself out of the interconnected modern world. And yet that outcome appears increasingly likely, as the British Parliament prepares to resume debate on a draft withdrawal agreement that has meager support.

In a no-deal scenario, London’s powerful banks could find themselves in legal limbo when they want to trade in Europe’s market. Millions of British citizens who have lived and worked in the E.U. legally for years, as well as E.U. nationals in Britain, could suddenly become undocumented. Connections between British and European law enforcement agencies would go dark.

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British leaders have warned of shortages of food and medicines, and they have asked importers to build stockpiles. Defense Secretary Gavin Williamson has put 3,500 troops on standby to deal with potential disruptions. In all, cabinet ministers have approved $2.5 billion of contingency spending.

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The countries that will remain in the European Union also are amping up their no-deal preparations. Irish lawmakers may have to set aside all other business this month to pass 45 pieces of emergency legislation aimed at mitigating the impact of Brexit. France is building roads, warehouses and checkpoints near its ports in preparation for new customs controls.

The E.U.’s headquarters in Brussels unveiled a list of proposals to protect E.U. citizens from the worst consequences of a no-deal Brexit, but that would offer little relief to the British side. British airlines, for example, would be able to carry passengers to E.U. airports only from Britain.

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Here in the Netherlands, exports to Britain could fall by 17 percent if Brexit happens without a deal, according to a study from the Organization for Economic Cooperation and Development.

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The Dutch government is scrambling to limit the damage, hiring nearly 1,000 more customs agents for the inspections that would become necessary. The agency, whose officials inspect meat, dairy products and animals, is scouring Eastern Europe for veterinarians and giving them crash courses in Dutch because they cannot find enough qualified people at home. And a legion of Dutch farmers and flower growers who take orders from British customers are worried that their supply lines could get tangled in bureaucratic knots.

“It’s all fresh, so you need to be able to deliver on very short notice,” said Pim Leenheer, who works in sales at a Dutch company, DailyFresh Logistics, that organizes food and flower shipments to Britain.

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On a gusty afternoon last month, tractor-trailers were arriving as little as 15 minutes before the vast Stena Hollandica ferry — which can hold 3.5 miles of trucks — pulled away. At the other end of the journey, in the British port of Harwich, the ferry can unload in 30 to 45 minutes, said Annika Hult, who directs North Sea shipping for the Stena Line.

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The process goes quickly in part because no customs agents are involved. In 1993, countries that belonged to what was then called the European Economic Community pulled down their customs posts and stopped checks between countries.

Little would change if British lawmakers approve the withdrawal deal negotiated by the E.U. and Prime Minister Theresa May. Britain would remain inside the E.U. customs union at least until new trade agreements are devised.

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But Britain’s leaving with no deal in place would set trade back decades.

“All of a sudden, you’re going to have certain checks,” Hult said.

Businesses would need to file paperwork with E.U. and British customs agencies when they want to send shipments between countries. Food and animals would need inspections on both sides. Truck drivers already pass through passport checks, since Britain is not a member of Europe’s passport-free travel area, but the post-Brexit checks would be far stricter. Dutch lawmakers are digging into their archives to figure out which old treaties with Britain might still be in force. Some date to the 1940s and 1950, when Europe was rebuilding after World War II.

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Some shipping and logistics companies expect that what currently takes a day to get to Britain could take a day and a half — a dramatic increase for a system whose margins of error are measured in minutes. They also fear the roads leading to the ports will turn into parking lots. At present, there is no overflow space for trucks that cannot be driven straight onto ships. There has been no need.

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“It’s like a queue in the supermarket. If the queue gets just a little bit larger than the capacity of the cashiers, the queue expands exponentially,” said Pieter Omtzigt, a Dutch lawmaker who is responsible for his country’s Brexit preparations.

Hult said operators of ferries such as hers were ready to find ways to speed any customs checks — if only they knew what to expect.

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“The challenge here is the lack of clarity,” she said. “If there’s certainty about what the framework is going to look like, and if the systems are there, we can act quite fast.”

The agencies that will have to do the inspections are bracing for complications.

“The feeling is that we are doing what we can to be prepared as possible, but I won’t say that there won’t be any incidents in the first weeks,” said Jan Meijer, director of inspection at the Netherlands Food and Consumer Product Safety Authority.

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Dutch authorities estimate that 35,000 small and medium-size Dutch businesses do business with Britain but have no experience with customs, since they keep their commerce inside the E.U. They would either have to navigate the complicated new terrain or cut off ties to Britain. The government is trying to get them ready. It is as if Illinois businesses suddenly need to contend with an international frontier to trade with Indiana — and have less than three months to figure out how to do so.

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“If we are preparing and companies are not preparing, then everything breaks down,” said Nanette van Schelven, director general of the Dutch customs authority. The agency has been running disaster drills to prepare for chaos.

“That’s basically the motto of this government: Hope for the best and prepare for the worst,” she said.

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But Dutch policymakers are nervous that Dutch businesses may still be too complacent.

“There’s still a lot of rationalizing going around, saying, ‘Things surely wouldn’t get that bad, would they?’ ” said Rem Korteweg, a senior research fellow at Clingendael, the Netherlands Institute of International Relations, who has advised Dutch lawmakers and businesses about preparations for Brexit. “There’s a lot of wishful thinking going around, and that’s a problem.”