UK warns France it could retaliate if she goes ahead with threats amid a row over post-Brexit fishing rights
France said it could stop UK boats landing in its ports if the row over licences was not resolved by Tuesday.
The UK government warned it could start “rigorous” checks on EU fishing activities in response.
And it has summoned France’s ambassador for talks later on Friday.
Boris Johnson will also have a “brush by” meeting with French President Emmanuel Macron at the G20 summit in Rome this weekend, the prime minister’s spokesman said.
He added that France remained a “close and strong ally” to the UK.
A British trawler was seized by France and another fined during checks off Le Havre on Thursday.
French authorities say the detained Cornelis Gert Jan vessel did not have a licence – a claim denied by the boat’s owner Macduff Shellfish of Scotland. But the European Union said the UK authorities withdrew the licence on 1 March.
The captain of the scallop dredger will face a court hearing in August next year, French authorities said on Friday.
BBC political correspondent Nick Eardley said No 10 sources were “amazed and concerned” at the escalating fishing row, describing the developments in recent days as “extraordinary”.
Ministers met on Thursday to discuss the situation and are understood to be considering a “range of options” to retaliate.
France was angered by a decision from the UK and Jersey last month to deny fishing licences to dozens of French boats to access British waters, and argued that this breached the Brexit deal.
The country has warned it would block British boats from landing their catches in some French ports next week and tighten checks on UK boats and trucks if the dispute over fishing licences was not resolved by 2 November.
France has also warned it could cut electricity supplies to Jersey, a British Crown dependency, as it previously threatened in May.
Brexit minister Lord Frost said the EU would be in breach of the UK-EU post-Brexit agreement if France were to disrupt UK fisheries, wider trade or energy supplies after Tuesday.
And ministers are considering launching “dispute settlement proceedings” with the EU if France goes ahead with the “unjustified measures”, a government spokesman said.