The UK is sending two Royal Navy boats to Jersey “as a precaution” after threats of a French blockade of the island’s main port.

Downing Street confirmed Boris Johnson spoke to Chief Minister of Jersey Senator John Le Fondre on Wednesday evening “about the prospect of a blockade of Saint Helier” – the island’s main town.

“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,” a Downing Street spokesman said.

“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.”

It comes after France threatened to cut the island’s electricity off over a post-Brexit fishing row.

France accused the UK on Wednesday morning of using red tape to limit fishing around Jersey, in breach of the Brexit agreement made with the EU last year, and said it is “ready to use these retaliation measures”.

“With regards to Jersey, I would remind you, for example, of electricity transmission by underwater cable. So, we have the means,” French maritime minister Annick Girardin said.