ITV News Political Correspondent Harry Horton explains what happens next in the growing row
Boris Johnson and Emmanuel Macron shared a fist bump at the G20 meeting in Rome on Saturday, but their friendliness comes against a backdrop of growing tensions between the UK and France.
As cross-Channel tensions rise, the government has signalled it's now "actively considering" starting legal proceedings against France due to its threats over fishing licences.
Why the threat of legal action?
Brexit minister Lord Frost warned the European Union it would be "in breach of its obligations" under the post-Brexit trade deal with the UK if Paris carries out threats to block British boats from landing their catch at French ports while tightening checks on vessels.
France has given the UK until Tuesday to grant more licences for small French boats to fish in British waters or face border and port sanctions.
The UK has warned France that, if it does act next week, then it is prepared to kick-start legal proceedings, arguing that Paris will have violated the terms of the trade agreement with Brussels.
What has the UK government said?
Both Boris Johnson and Lord Frost have stepped up their lobbying of the EU in a bid to encourage bloc leaders to pull France back from its proposed reaction.
In a meeting with the EU’s top official, Ursula von der Leyen, at the G20 in Rome, Downing Street said the PM warned that the threats did "not appear to be compatible with the UK-EU Trade Co-operation Agreement (TCA) or wider international law".
The comments came after Mr Johnson refused to rule out triggering the dispute mechanism resolution clause in the trade agreement - which could result in fines or even the treaty being suspended - if France does not back down.
Lord Frost on Saturday rallied against comments made by French prime minister Jean Castex in a letter to European Commission president Ms von der Leyen, that the UK should be shown "it causes more damage to leave the EU than to stay in".
The Tory peer tweeted: "To see it expressed in this way is clearly very troubling and very problematic in the current context when we are trying to solve many highly sensitive issues, including on the Northern Ireland Protocol.
"This is all the more so as the threats made by France this week to our fishing industry, to energy supplies, and to future co-operation, for example through the Horizon research programme, unfortunately form part of a pattern that has persisted for much of this year.
"As I set out yesterday to (European Commission vice-president) Maros Sefcovic, these threats, if implemented on November 2, would put the EU in breach of its obligations under our trade agreement.
"So we are actively considering launching dispute settlement proceedings as set out in Article 738 of the TCA."
So why the friendliness between Johnson and Macron?
The Prime Minister and French president Emmanuel Macron are due to talk on the margins of the G20 summit this weekend, with suggestions they could meet on Saturday.
During broadcast interviews in Rome, Mr Johnson left the door open to finding a resolution with Mr Macron as he described the UK as being "very keen to work with our friends and partners".
Mr Johnson repeated the statement he made on the plane over to Italy, vowing to "take steps to protect UK interests" if there is a breach of the TCA with the EU.
What has the EU said?
In comments made before the Rome talks, a commission spokesman said the trade deal made provision that "vessels who were fishing in these waters before (Brexit) should be allowed to continue" and implored Britain to look at each case, "boat-by-boat".
The wrangle over fishing access escalated this week after French authorities detained a Scottish-registered scallop dredger after accusing it of fishing without a licence.
The captain of the Cornelis Gert Jan vessel, understood to be an Irish national, has been told to face a court hearing in August next year.
Foreign Secretary Liz Truss took the rare step of ordering an allied nation’s envoy to be summoned as she called Catherine Colonna, French ambassador to the UK, to the Foreign Office on Friday afternoon to challenge her over France’s stance.