The UK Government has threatened to retaliate should France impose sanctions on British fishing vessels, amid reports that one has been detained.
Environment Secretary George Eustice said threats to block British boats from French ports and tighten checks appear to breach international law.
The UK will deliver an “appropriate and calibrated response” if France follows through with the measures, the Cabinet minister warned.
Mr Eustice also confirmed that his officials are “urgently” investigating reports that a British trawler has been detained off the coast of France as disputes about fishing rights continue.
Mr Eustice’s Cabinet colleague Priti Patel described the incident as “disappointing”.
When asked whether she had spoken with her French counterpart, the Home Secretary told the PA news agency: “It is disappointing, and we as a country fulfilled all our obligations under the Trade and Co-operation Agreement (TCA).
“But at the same time, discussions across Government will continue, both at commission level but also with counterparts within the French administration.”
French authorities said the UK’s failure to comply with trade agreements is “unacceptable” and they will defend the rights of their own fishermen.
It comes after two boats were fined on Wednesday when one failed to comply with checks by police and the other was found not to hold a proper licence.
A statement from the French maritime ministry said checks had been carried out on the boats in the Baie de Seine, near Le Havre, in the north of the country.
One trawler was fined for obstructing checks after it initially refused a request to be boarded by police, the statement said.
It was later found not to have been in breach of regulations.
The ministry said the second boat was not on a list of UK vessels with licences granted by the European Commission and France.
The boat was then ordered to divert to Le Havre.
Mr Eustice told MPs: “What I’ve been able to establish so far in respect of that vessel is that they were on the list that was provided by the MMO (Marine Management Organisation) initially to the European Union.
“The European Union therefore did grant a licence. We are seeing some reports that, for some reason, they were subsequently withdrawn from the list; it’s unclear why that might have been at the moment.”
Earlier, France’s Europe minister, Clement Beaune, told French TV news channel CNews: “We have been extremely patient… our fishermen have been extremely responsible… And so, from November 2, it’s over: we will engage in dialogue if the British want to, but we are taking retaliatory measures.”
He added: “Now we need to speak the language of force because, unfortunately, that seems to be the only thing this British Government understands.”
French maritime minister Annick Girardin also told French radio news programme RTL Matin that Britain’s “failure to comply” with the Trade and Co-operation Agreement (TCA) is “unacceptable”.
“It’s not war, it’s a fight,” she said.
“The French and the fishermen have rights. An agreement was signed.
“We must enforce this agreement. We have fishing rights, we must defend them and we will defend them.”
But Mr Eustice said the UK has licensed 98% of EU vessels that have applied for access post-Brexit and more are expected to be granted following “constructive” talks with the European Commission.
He noted that he had told France and the European Commission that the UK’s “door remains ever open”.
But he added: “In that context it is very disappointing to see the comments that came from France yesterday. We believe these are disappointing and disproportionate, and not what we’d expect from a close ally and partner.
“The measures being threatened do not appear to be compatible with the Trade and Co-operation Agreement or wider international law, and, if carried through, will be met with an appropriate and calibrated response.”