Environment Secretary George Eustice has said the Government is trying to get to the bottom of exactly why a Scottish fishing vessel was detained by French authorities.

The Cornelis Gert Jan was detained at Le Havre amid a dispute over post-Brexit fishing rights.

Speaking to the BBC’s Good Morning Scotland programme on Friday, Mr Eustice said the scallop trawler was originally on a list of approved vessels but appeared to have been taken off, but was nevertheless entitled to fish in the waters.

He said: “We’re trying to get to the bottom of what happened. It is true that it was on the list originally and it had a licence.

“We understand that what happened is it may have made some changes to the engine on the vessel, and that meant that the licence had to be renewed.

“We’re trying to get to the bottom, working with Marine Scotland and the MMO and the owners of the vessel, to understand why it dropped off the list.

“But this is a minor administrative thing. I think it is entitled to fish in those waters.”

READ MORE: Nigel Farage tells UK Government to hit back after Scottish trawler is seized by French

Mr Eustice added that France had decided to “politicise” the process of checking vessels this week.

Britain has told France “two can play at that game” in a warning the UK could retaliate if Paris goes ahead with “inflammatory” threats made in a post-Brexit row over fishing rights.

Foreign Secretary Liz Truss will challenge Paris’s ambassador to the UK Catherine Colonna on France’s intentions on late on Friday afternoon after taking the rare step of ordering an allied nation’s envoy to be summoned.

French ministers have 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.

George Eustice did not rule out blocking French vessels in return as he struck out at a claim from France’s Europe minister Clement Beaune that the only language Britain understands is “the language of force”.

Earlier, Mr Eustice told BBC Breakfast: “That is completely inflammatory and is the wrong way to go about things.”

Catherine Colonna French Ambassador to the UK Catherine Colonna (Dominic Lipinski/PA)

Asked how the UK will respond if France does go ahead and block British trawlers, the Cabinet minister said: “Two can play at that game.”

He insisted any British response would be “proportionate”, adding: “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.”

Pressed if the Government could block French vessels landing their catches in the UK, he responded: “If the French obviously do continue with this, then yes, we will take a proportionate response to that.”

Mr Eustice acknowledged that the France detaining the British vessel may have been a “routine operation” but has received mainstream attention because French authorities last week “said they were going to introduce all sorts of problems and make life difficult for people”.

Britain has said France’s threat would likely breach EU law and Ms Truss has said she will ask the ambassador “to explain the disappointing and disproportionate threats made against the UK and Channel Islands”.

READ MORE: Crew of seized Scottish scallop trawler Cornelis Gert Jan in 'good spirits' after France arrest

UK ministers met on Thursday 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.

The Government views the proposed actions as “unjustified” and questioned whether they were compatible with the UK-EU trade deal “or wider international law”.

A UK Government spokesman added: “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 scallop vessel Cornelis Gert Jan was caught up in the diplomatic storm, and ordered to divert to the port of Le Havre on Wednesday after the French authorities said it was fishing in French waters without a licence.

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

The owner of the Cornelis, Macduff Shellfish, said the vessel had been fishing legally in French waters and called on the British Government to protect the rights of British fishermen.

Andrew Brown, director of sustainability and public affairs at Macduff, said: “It appears our vessel has been caught up in the ongoing dispute between the UK and France on the implementation of the Brexit fishing agreement.”

On Thursday, Mr Eustice told MPs the vessel had been granted a licence by the EU but that there were reports that it subsequently had been removed from the list of vessels permitted to fish in French waters for reasons that were unclear.

The Herald:

The ship in port 

Earlier, Mr Beaune told French TV news channel CNews: “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 UK-EU Trade and Co-operation Agreement (TCA) is “unacceptable”.

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

“We have fishing rights, we must defend them and we will defend them.”

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.

Mr Eustice told MPs on Thursday 171 vessels have been licensed to fish in the UK six to 12 nautical mile zone, of which 103 are French, and 18 of those vessels are under 12 metres.