THE UK IS “actively considering” starting legal proceedings against France due to its threats over fishing licences as cross-Channel tensions deteriorated.

Brexit minister David Frost has 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 its 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.

But 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.

Both Boris Johnson and David 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 Prime Minister 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 Johnson had 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.

Frost on Saturday repeated his assertion that the UK was prepared to commission legal action as a result of the fishing dispute.

In a series of tweets, the Conservative peer rallied against comments made by French prime minister Jean Castex in a letter to European Commission president von der Leyen, that the UK should be shown “it causes more damage to leave the EU than to stay in”.

Frost said: “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.”

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 interviews in Rome, 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”.

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.

At the centre of the dispute are the licences for small boats, which are issued only if the vessels can demonstrate a history of fishing in British waters.

According to No 10, Johnson stressed during his conversation with von der Leyen that the UK was “happy to consider any further evidence” for licence applications which had been rejected. The UK has said only 2% of EU licence bids had been denied.

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.