This video can not be played
The UK has condemned "unjustified" threats from France and summoned the country's ambassador, in an escalating row over post-Brexit fishing rights.
Foreign Secretary Liz Truss is calling for talks on Friday, asking the ambassador to explain "disappointing and disproportionate threats".
A British trawler was seized by France and another fined during checks off Le Havre overnight into Thursday.
French authorities said the detained vessel did not have a licence.
However, Environment Secretary George Eustice has insisted the European Union did grant a licence to the trawler and said it was "unclear" why, according to reports, it was subsequently withdrawn from the list given to the EU.
France was angered by a decision from the UK and Jersey last month to deny fishing licences to dozens of French boats, and argued that it breached the Brexit deal.
The country has warned it would block British boats from some ports next week and tighten checks on UK boats and trucks if the dispute over fishing licences was not resolved by 2 November.
It issued its ultimatum on Wednesday evening, saying it would begin to impose "targeted measures" from next Tuesday, including preventing British fishing boats from disembarking at ports and more checks on UK goods.
France has also warned it could cut electricity supplies to Jersey, a British Crown dependency, as it previously threatened in May.
- Who really owns UK fishing rights?
- What does the Brexit deal mean for fishing?
Ms Truss tweeted on Thursday evening: "I have instructed Europe Minister Wendy Morton to summon the French ambassador to the UK for talks tomorrow to explain the disappointing and disproportionate threats made against the UK and Channel Islands."
And Brexit minister Lord Frost has chaired a meeting to consider the UK government's response to the row.
A government spokesman said: "The proposed French actions are unjustified and do not appear to be compatible on the EU's part with the Trade and Co-operation Agreement (TCA) or wider international law.
"We regret the confrontational language that has been consistently used by the French government on this issue, which makes this situation no easier to resolve."
The spokesman added the concerns had been raised "strongly" with the French and the EU Commission.
This video can not be played
The detained vessel has been named as the Cornelis Gert Jan.
Its owner, Macduff Shellfish of Scotland, said the vessel was fishing legally in French waters and called on the UK government to protect the rights of British fishermen.
The firm's Andrew Brown said it appeared the Cornelis, based at Shoreham, in West Sussex, had been "caught up" in the ongoing UK-France post-Brexit fishing row.
He warned that without "a speedy resolution", the vessel's catch could be confiscated by the French authorities, and called on the UK government to "defend the rights of the UK fishing fleet".
The firm would "vigorously defend" itself against any claims, but its "priority concern" was for the welfare of the vessel's crew, he said.
French maritime minister Annick Girardin said on Twitter the trawler was found to be fishing in the Bay of Seine without the proper licences.
The minister said checks on the British vessels were standard during the scallop fishing season.
But she added they had also been undertaken against "the backdrop of the tightening of controls in the Channel, in the context of discussions on licences with the United Kingdom and the European Commission".
The UK maintains the rejected applications that sparked the row did not have enough supporting evidence to show the boats had a history of fishing in Britain's or Jersey's waters.
A meeting with officials from France, Jersey, the UK and European Commission on Wednesday led to 162 French boats being given licences to fish in Jersey's waters from Friday.
The government of Jersey said it was "extremely disappointed" by the latest threats of sanctions by France. French trawlers previously protested outside the port of St Helier on the island.