Why has the French ambassador been summoned by the UK government?

France’s ambassador to the UK has been summoned to the Foreign Office as the row over post-Brexit fishing rights dramatically escalated.

Foreign secretary Liz Truss took the rare step of ordering an allied nation’s envoy to be summoned in a sign of the UK’s concern about the row, which has already seen one UK trawler detained in a French port.

France claims there is a lack of licences for French boats to fish in UK waters and has warned they will block British boats from some French ports and tighten checks on vessels travelling between France and the UK if the issue is not resolved by Tuesday – as well as threatening the electricity supply to the Channel Islands.

Here's what's going on:

What is the Brexit Fisheries Agreement?

France says the UK and the Channel Island of Jersey have turned down applications from dozens of French boats to fish in their waters in what Paris said was a breach of Britain’s post-Brexit trade deal with the EU.

The fishing agreement was part of the post-Brexit trade deal between the UK and the EU, and was one of the most difficult parts of negotiations.

Watch: Brexit fishing row explained: Why are the UK and France fighting?

It allows EU boats to fish in UK waters but gave the UK more of the share of fish – which will rise over the coming years.

After the taper there will be annual negotiations to decide how catches are shared between the UK and EU.

What has the French government said about the dispute?

France has said if the situation is not resolved they will begin imposing sanctions on British fishing from 2 November.

Authorities said the UK’s failure to comply with trade agreements is “unacceptable” and they will defend the rights of their own fishermen.

Read more: Boris Johnson's government surprised EU 'rigidly' sticking to Brexit rules

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 2 November, it’s over: we will engage in dialogue if the British want to, but we are taking retaliatory measures.”

This could include blocking British boats from some French ports and tightening checks on vessels travelling between France and the UK

He 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 Britain’s “failure to comply” with the Trade and Co-operation Agreement (TCA) is “unacceptable”.

“It’s not war, it’s a fight,” she said.

On Wednesday, a UK scallop vessel – the Cornelis Gert Jan – was caught up in the diplomatic storm and ordered to divert to the port of Le Havre after French authorities said it was fishing in French waters without a licence.

The French said that another British trawler had also been fined for obstruction after refusing to allow police to board to carry out checks.

What has been the UK response?

On Thursday evening, France’s ambassador to the UK, Catherine Colonna, was summoned to the Foreign Office where she will be questioned on Friday about the threats of retaliation by Paris.

Ms Truss said: “I have instructed Europe minister Wendy Morton to summon the French ambassador to the UK for talks… to explain the disappointing and disproportionate threats made against the UK and Channel Islands.”

Earlier, UK ministers had met to consider the response, with the prospect of tit-for-tat action if France carries out its threats.

Brexit minister Lord Frost, who chaired the meeting, said: “I remain concerned by French plans on fisheries and beyond”, adding that “we expect to have more to say” on Friday.

Environment secretary George Eustice has accused France of “inflammatory language” and did not rule out blocking French vessels from landing their catches in the UK in retaliation.

Asked about the claim that the only language Britain understands is “the language of force”, Eustice told BBC Breakfast on Friday: “That is completely inflammatory and is the wrong way to go about things.

“We will see what they do on Tuesday but we reserve the right to respond in a proportionate way.

"Two can play at that game."

“It’s always open to us to increase the enforcement we do on French vessels, to board more of them if that’s what they’re doing to our vessels, there are other administrative things we can require of vessels.”

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Eustice maintains the UK has licensed 98% of EU vessels that have applied for access post-Brexit and more are expected to be granted following “constructive” talks with the European Commission.

France insists that around half of licences relating to the disputed waters around Jersey have not been granted.

What will happen next?

It's hard to say, the both the UK and France are ramping up their war of words right now mostly to appeal to their domestic audiences.

This could involve routine checks on British ships, banning some vessels from French ports, and tightening up of controls around lorries to and from the UK.

Whatever happens ultimately, the UK and France are very close allies and, despite Brexit, have remained committed to each other.

It is likely the EU will work with the UK to broker an agreement to avoid any further escalation.

Some have suggested that French president Emmanuel Macron facing a difficult re-election challenge may be a “factor” in the fishing row.

Eustice said Boris Johnson could raise the fishing row with Macron at the G20 in Rome.

Will supplies of fish to the UK be affected by the dispute?

It's unlikely. The UK imports huge amounts of its fish from foreign countries and British fishermen often sell their goods abroad.

If the row ever escalated to such an extent British fishermen were completely unable to fish around France then UK retailers would likely be able to fill the gap via other imports.