Two Royal Navy vessels are patrolling waters around Jersey amid concerns of a possible blockade of the island due to an ongoing row with France over post-Brexit fishing rights.

HMS Severn and HMS Tamar have been deployed by the UK Government to “monitor the situation” at the Channel Island amid a protest by French fishing vessels at the port of St Helier over the lack of access.

French maritime minister Annick Girardin warned on Tuesday that the country is ready to take “retaliatory measures”, accusing Jersey of dragging its feet over issuing new licences to French boats.

Prime Minister Boris Johnson spoke to Jersey Chief Minister Senator John Le Fondre and External Affairs Minister Ian Gorst on Wednesday, and “underlined his unwavering support” for the island.

Dozens of French boats arrived at the harbour on Thursday morning, with some crews setting off flares during the so far peaceful protest, according to the Jersey Evening Post.

The newspaper later said the leader of the protest had asked the French boats to leave the harbour to let a freight ferry, the Commodore Goodwill, depart.

Jersey fisherman Josh Dearing described the scene at the port of St Helier on Thursday morning as “like an invasion”, with the French fleet mostly made up of “big French dredgers and trawlers” of 12 metres or more.

It was quite a sight. It was like an invasion

The 28-year-old told the PA news agency: “There were probably about 60 boats. There were a few hand-held flares and smoke flares going off and apparently a few maybe bangers and stuff going off from the French.

“It was quite a sight. It was impressive, I looked from the shore this morning and it was just like a sea of red lights and flares already going off at sea. It was like an invasion.”

Paris has warned it could cut off power to the island, which receives 95% of its electricity from France through three undersea cables, in retaliation for the fallout.

A Ministry of Defence spokesman said: “HMS Severn and HMS Tamar are deploying to Jersey to conduct maritime security patrols.

“This is a strictly precautionary measure and has been agreed with the Jersey Government.”

A Downing Street spokesman added: “The Prime Minister and Chief Minister stressed the urgent need for a de-escalation in tensions and for dialogue between Jersey and France on fishing access.

“The Prime Minister underlined his unwavering support for Jersey.

“He said that any blockade would be completely unjustified.

“As a precautionary measure the UK will be sending two offshore patrol vessels to monitor the situation.

“They agreed the UK and Jersey Governments would continue to work closely on this issue.”

Don Thompson, president of the Jersey Fishermen’s Association, said his members have warned they are prepared to ditch their fishing licences if the French win their demands.

He told Good Morning Britain: “We’ve already told our minister – our licences, some of our fishermen have paid a quarter of a million pounds for our licences – we’re going to get rid of our licences and fish without licences.

“We just will not put up with those (French) boats being left to fish uncontrolled, unsustainably in our waters, whilst we’re subject to all sorts of constraints.”

Speaking to BBC Newsnight on Wednesday, Mr Gorst said: “We take these threats from both Paris and the French fishermen very seriously.

“They are disproportionate to the issues that are being experienced in the post-Brexit trade licensing issuing.”

The row began after the island implemented new requirements under the terms of the UK-EU trade deal for boats to submit evidence of their past fishing activities in order to receive a licence to carry on operating in Jersey waters.

On Wednesday, Mr Gorst held talks with Marc Lefevre, the president of the La Manche region of northern France, on the “difficult set of issues relating to fishing licences”.

“There are a number of important matters which we will continue to work through,” he said.

Ms Girardin told the French parliament that it gave Paris the “means” to act against the island if the issue could not be resolved.

“Even though I am sorry that it has come to this, we will do so if we have to,” she said.

Mr Gorst, however, said the island is not seeking to bar boats which have historically fished in Jersey waters and insisted the dispute can be resolved amicably.

He said that of the 41 boats which sought licences under the new rules last Friday, all but 17 had provided the evidence required.

“The trade deal is clear but I think there has been some confusion about how it needs to be implemented, because we absolutely respect the historic rights of French fishermen to fish in Jersey waters as they have been doing for centuries,” he said.

“I do think a solution can be found.

“I am optimistic that we can provide extra time to allow this evidence to be provided.”