The EU has complained to Britain that the terms of its post-Brexit trade deal are being ignored in the deepening dispute over fishing rights off Jersey.
The European Commission said French fishing boats were facing “additional conditions” if they were to carry on operating, in breach of the terms of the agreement hammered out on Christmas Eve.
But in a call with Jersey’s chief minister John Le Fondre, Boris Johnson again voiced his “unequivocal support” for the actions taken by the island’s government.
He said two Royal Navy patrol boats despatched to the area on Wednesday would remain in place as a “precautionary measure”.
Meanwhile, the French authorities said they were sending a pair of police patrol boats as dozens of protesting French fishing vessels gathered off the main port, St Helier.
The row erupted after the Jersey government said French boats would be required to obtain licences to carry on fishing in the island’s waters under the terms of the trade deal with the EU which came into force last Friday.
The move provoked a wave of anger among French fishing communities who complained that some boats which had operated there for years were suddenly having their access restricted.
In Brussels, a spokeswoman for the European Commission said “additional conditions” attached to the new licences represented a breach of the trade deal.
“We have… indicated to the UK that we see that the provisions of the EU/UK Trade and Co-operation Agreement, that we recently agreed, have not been met there, have not been respected,” the spokeswoman said.
Jersey’s external relations minister, Ian Gorst, said representatives of the island’s government were meeting the French fishermen in an attempt to defuse the worsening row.
“It’s important that we respond to threats, but the answer to this solution is to continue to talk and diplomacy,” he told BBC News.
Downing Street announced on Wednesday that the patrol boats HMS Severn and HMS Tamar were being sent to the island following warnings French fishing boats could try to blockade St Helier.
In turn the French maritime authority for the Channel and the North Sea said the patrol boats Athos and Themis were being sent to the island “to ensure the protection of human life at sea”.
A spokeswoman said they were being stationed to be in a position to intervene “as quickly as possible” if the situation worsens.
Local fishermen reported around 60 French boats had gathered off St Helier early on Thursday, with some entering the harbour before leaving after an hour.
In the course of the protest, a Jersey fishing boat was reportedly rammed by a French vessel, before the French fishermen headed back to France.
Dimitri Rogoff, who heads a group of Normandy fishermen, insisted they were not seeking to blockade the port.
“This isn’t an act of war. It’s an act of protest,” he told the Associated Press news agency.
Nevertheless, there was concern on the island that the French action could escalate if the dispute was not resolved.
Fisherman Josh Dearing described the appearance of the French boats, some letting off flares, as “like an invasion”, and welcomed the presence of the Royal Navy ships.
“We’re completely unprotected in Jersey. We’ve got nothing except for a few police officers. We don’t have a police boat, we don’t have a navy boat, we don’t have anything to protect us,” he told the PA news agency.
“The French can be hostile. All of our livelihoods are in that harbour and if they wanted to they could cause damage.
“They can blockade their own harbours – they wouldn’t think twice about coming and doing it to us.”
Earlier this week French maritime minister Annick Girardin said Paris would cut off electricity to Jersey – which gets 95% of its power supply from France – if the dispute was not resolved.
Mr Gorst said Jersey authorities were “extremely grateful” for the support of the UK Government, while stressing the need to find a diplomatic resolution.
“We’ve heard disproportionate threats from Paris and now with a potential blockade, but the answer to the issues that are being faced are without doubt talking and diplomacy,” he said.
The Jersey government has said that of the 41 French boats that applied for licences last Friday, 17 had been unable to provide the evidence needed to enable them to carry on as before.
Mr Gorst said: “It’s really important that we are able to work with those fishermen to help them provide the necessary evidence so that, if required, their licences can be amended.”