The British government has warned France that it risks breaking the Brexit trade deal, as Emmanuel Macron's government continues to detain a UK fishing vessel.
French maritime authorities overnight fined one UK vessel and detained another, for allegedly not having the right licence to fish.
Responding to the agreement on Thursday morning UK environment secretary George Eustice said France's threats to take further action "do not appear to be compatible with a trading cooperation agreement or wider international law".
He said the boat in question appeared to have been issued with a fishing licence but then had it withdrawn, and that the situation was "unclear".
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 We are seeing some reports that, for some reason, they were subsequently withdrawn from the list; it's unclear why that might have been at the moment."
The incident overnight on Wednesday and Thursday came after threats by the French government to retaliate against the UK for blocking fishing licences in the Channel Islands.
France says the licences for its vessels are guaranteed under the Brexit deal and that the UK's policy amounts to breaking the agreement. It has threatened to take wider measures including further crackdown on UK fishing, changes to energy supplies, and possible disruption to the UK landing goods in French ports.
Earlier on Thursday, 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."
Mr Beaune 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 the UK's "failure to comply" with the Brexit deal was "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."
Speaking in the Commons on Thursday Mr Eustice said the UK would not "get into a retaliatory tit for tat on this kind of thing", adding: "It's important that everyone remains calm."
He said there was no reason to be concerned about the crew and that it was the understanding of the British government that the boat was still being detained.
Ms Girardin said in a statement released on Thursday morning: “This Wednesday, two English ships were fined during classic checks off Le Havre. The first did not comply spontaneously... the second did not have a licence to fish in our waters”.
The French minister added that the ship was “diverted to the quay and handed over to the judicial authority”.
France is angry with the UK as it has not granted its fishermen the full number of licenses to operate inside British waters that it says are guaranteed under the Brexit deal.
The country said it would impose retaliatory measures that could come into effect from 2 November if there is no progress in talks between the countries.