LONDON — It wasn’t another Falklands War, let alone a modern-day battle of Trafalgar. Yet, when naval ships from Britain and France converged in the waters off the island of Jersey on Thursday, it was a vivid reminder of the loose ends left by Britain’s bitter departure from the European Union.

The maritime standoff came after 60 French fishing boats massed to blockade a port in Jersey in an ugly spat over post-Brexit fishing rights. By day’s end, tempers had cooled as both sides pledged to work out differences over new licensing requirements for the French fishermen who ply these coastal waters. The French protesters shot off flares and waved angry banners, then sailed away.

The sudden eruption of tensions in the English Channel, five months after Britain ratified its split with the European Union and on the eve of a British election, drew theatrical displays of muscle-flexing in London and Paris — suggesting it was a politically expedient six-hour clash, even if it augurs months or years of tensions ahead.

The dramatics began Wednesday evening when Prime Minister Boris Johnson deployed two Royal Navy vessels, the HMS Tamar and the HMS Severn. His office called it a “precautionary measure,” but it amounted to a vigorous show of support for Jersey, a crown dependency of Britain and the largest of the Channel Islands.

A day later, France answered with its own deployment of two naval patrol ships near the island, which lies just 14 miles off the French coast. French officials said they were sent to protect the “safety of human life at sea” in the crowded waters off Jersey’s capital, St. Helier. British papers published video of a French trawler ramming the stern of a British pleasure craft; no one was hurt.

Earlier in the week, a French government official warned that France could cut off the power supply to Jersey, most of which is delivered through undersea cables from France. That brought a derisive reaction from London, where officials muttered that even Germany hadn’t turned off the lights when it occupied Jersey during World War II.

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For Britain, which just played host to foreign ministers from the Group of 7 nations and is debuting its post-Brexit role in the world, a clash with France over fish in the English Channel seemed like a relic of a bygone age. But it also laid bare the risks of life outside the European Union.

“This is the kind of old-fashioned dispute that the European Union was created to prevent,” said Simon Fraser, the former top civil servant in Britain’s Foreign Office. “When you leave the European Union, you risk reopening them.”

Gérard Araud, a longtime French diplomat who served as ambassador to the United States, said, “What is happening in Jersey is, on the one hand, totally silly. Threatening to cut off the electricity makes no sense.”

Still, Araud said the indignant French reaction had a deeper subtext: The country’s sense of anger and loss at Britain’s departure from the European Union, where it had helped balance France’s relationship with Germany.

Relations had already soured on a range of issues as Britain finalized its divorce from the European Union. President Emmanuel Macron of France raised doubts about a coronavirus vaccine developed at the University of Oxford and produced by AstraZeneca, a British-based drugmaker, prompting charges of “vaccine nationalism.”

In December, Macron briefly cut off access to freight shipments to and from Britain to prevent a fast-spreading variant of the virus that originated in Britain from leaping across the English Channel.

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At issue in Jersey are new licensing requirements the authorities imposed on French fishing boats, which have long worked the waters around the Channel Islands. Among other things, the vessels are required to carry equipment that allows their locations to be tracked.

Under the part of the Brexit agreement governing fishing, which went into effect on May 1, following a four-month grace period, Jersey granted fishing licenses to 41 French boats larger than 12 meters, or 39 feet. The problem, according to Marc Delahaye, director of the Normandy Regional Fisheries Committee, was that the additional requirements were imposed without warning or consultation. The European Commission said the British government had notified it of the changes last week and that it was in discussions with London.

As a crown dependency, Jersey is not part of the United Kingdom and has special status that gives it self-governing rights, including its own Legislative Assembly, as well as fiscal and legal systems. However, Jersey’s reliance on French electricity makes its economy vulnerable, Delahaye said, noting that it was in the interests of the British and French governments to calm the situation.

“I don’t think that London and Paris want to start firing missiles across the Channel,” he said.

France’s Europe minister, Clément Beaune, said Thursday that France also wanted a quick easing of tensions and the implementation of the Brexit trade agreement. But he told Agence France-Presse, “We won’t be intimidated by these maneuvers.”

While the dispersal of the French fishing boats defused the immediate crisis, authorities in Jersey have yet to grant licenses for smaller French vessels. Fishing, therefore, could remain a flash point.

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For Johnson, however, the timing of the clash arguably could not have been better. Voters went to the polls in Britain on Thursday in local and regional elections that are viewed as a referendum on his Conservative Party after Brexit and a year of the pandemic. News that he had deployed navy warships, bristling with machine guns, pushed aside a skein of reports about his ethical conduct while in office.

“Our New Trafalgar,” said a headline in the online edition of the Daily Mail, referring to the 1805 battle in which the Royal Navy vanquished the navies of France and Spain and established Britain’s maritime supremacy. One of the French patrol boats, the Athos, was much smaller than the British warships, it noted.

On Thursday, Johnson called the chief minister of Jersey, John Le Fondré, to reiterate “his unequivocal support for Jersey,” according to a readout from Downing Street. Hours later, the government declared the crisis “resolved for now” and said the two warships would prepare to return to port.

Fishing was one of the thorniest issues when Britain negotiated its new trade agreement with the European Union, which came into force in January. The deal ended decades during which Britain’s fishing fleet was under the same system as France, with their catches negotiated regularly among the member countries.

Many in Britain’s fishing industry supported Brexit because they believed that for decades, they had been forced to share too much of the fish caught in Britain’s coastal waters with continental crews.

But the agreement sealed by Johnson and negotiators in Brussels just before Christmas was a disappointment to British fishing communities, who had been promised a “sea of opportunities” by Brexit supporters.

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Instead, the increase in annual quotas for British fishing crews was initially modest. And because Britain has left Europe’s single market for goods, British fish and shellfish require more documentation and checks when sent to markets in continental Europe, making them more difficult and expensive to export.

Fishing rights have long provoked acute tensions between Britain and its neighbors. From the 1950s to the 1970s, Britain was embroiled in a confrontation with Iceland that became known as the “cod wars.” At its peak, 37 Royal Navy vessels were mobilized to protect British trawlers in disputed waters.

While none of these clashes have mutated into broader military conflicts, diplomats said there was always a risk of accidental escalation.

“This is not going to settle down,” said Barrie Deas, the chief executive of the National Federation of Fishermen’s Organizations. “Fish will be a source of a toxic relationship for a long time, possibly for decades.”