Brussels has accused Britain of breaking the newly ratified EU-UK trade deal after French fishermen staged a seaborne protest outside Jersey’s main port over an escalating row over fishing rights that prompted London to send two naval vessels to the area.

The European Commission said the UK’s failure to justify and give advance warning about special conditions attached to licences issued by Jersey for fishing in the waters of the British Channel island dependency ran counter to its obligations under the trade agreement.

The dispute is the latest friction to arise between the two sides since Britain left the EU single market at the end of last year.

A spokesperson for the commission said Brussels had “indicated to the UK” that the provisions of the trade deal “have not been respected”.

But senior Downing Street officials disputed that the terms of the trade and co-operation agreement, ratified by the European Parliament last week, had been breached. “Jersey acted within the terms of the TC,” one senior Number 10 insider said.

“If the EU encounters a difficulty, as French fishermen seem to, rather than using threatening language — as some French ministers have — or trying to blockade a foreign port, they should use the dispute resolution mechanisms in the TCA, which the European Parliament has just ratified.”

Number 10 said the two Royal Navy patrol vessels would “remain in place to monitor the situation as a precautionary measure”.

UK naval vessels patrol the waters off Jersey

The waters around Jersey are covered by the fishing chapter of the EU-UK trade deal struck in the final days of 2020. The agreement sets out a system for maintaining some pre-Brexit fishing rights, including the possibility for boats that have a tradition of operating in coastal waters to continue doing so by applying for licences.

French fishermen have complained about being forced to provide electronic monitoring data to prove they have operated in Jersey waters before in order to receive a licence.

Small boat owners argue that they do not have GPS technology and the other electronic surveillance equipment required. Other special conditions attached to the licences relate to fishing gear.

The EU commission said that, under the trade deal, any changes to licensing rules “have to be based on a clear scientific rationale”, not discriminate between EU and UK boats, and “be notified in advance to the other party, [giving] sufficient time to assess and react”.

President Emmanuel Macron’s administration sought to lower the temperature on Thursday afternoon, with a senior official calling for a rapid solution to the Jersey problem and saying that any French retaliatory measures would be “a last resort” that Paris did not want to implement.

Clément Beaune, France’s Europe minister, said he had spoken to David Frost, his UK counterpart. “Our aim is not to keep tensions high but to have a rapid and complete application of the agreement,” he added.

After French threats this week to cut off the island’s electricity supply, two Royal Navy ships — HMS Tamar and HMS Severn — patrolled the waters off Jersey as dozens of French fishing boats arrived to protest against the restrictions on their activity. France also deployed two vessels along the maritime boundary between French and Jersey waters.

Under the terms of the post-Brexit trade deal, should the dispute persist either the EU or UK could request that an arbitration panel reviews the situation, backed with the threat of trade sanctions if the losing side does not comply with the panel’s ruling.

But Brussels said that its focus for now was to “engage constructively” to try to resolve the dispute. It called for “restraint and calm”.

Some 56 French fishing boats sailed to the port of St Helier on Thursday morning. Although some red flares were set off, the protests appeared to remain peaceful, and the boats returned to France in the afternoon.

“The show of force is done,” Dimitri Rogoff, who heads the Normandy regional fishing committee, told the French news agency AFP. “It’s now up to the politicians to do their work.”

Gregory Guida, a Jersey assistant minister, held a 90-minute meeting with French fisherman to listen to their concerns.

John Le Fondré, Jersey’s chief minister, said the government recognised the challenges of implementing the new trading arrangements.

“Speaking directly to the fishermen has enabled both parties to better understand how those challenges will be addressed, and we are proposing the establishment of a forum which will enable the government of Jersey to continue to engage with all fishermen in the region.”

Boris Johnson, UK prime minister, spoke to ministers in Jersey on Thursday, reiterating his “unequivocal support” for the island.

Number 10 said the Royal Navy patrol vessels would “remain in place to monitor the situation as a precautionary measure”.