THERESA May has led a Cabinet discussion on “strengthening the Union” as Downing Street made clear the concerns of the UK fishing industry about the implications of extending the 21-month transition period would be properly addressed.

The Prime Minister told her senior colleagues the United Kingdom was a “Union of nations, celebrating the rich cultural, economic and social benefits that each constituent part brings”.

Among those making contributions to the presentation on strengthening the Union were David Lidington, Mrs May’s de facto deputy, and David Mundell, the Scottish Secretary.

Asked why the PM and her colleagues felt the need at this time to discuss strengthening the Union, her spokesman said: “The whole point of Cabinet is to hold discussions across the whole range of issues relevant to the Government.”

Two weeks ago, Mrs May’s 11-strong inner War Cabinet talked through the issue of extending the transition period but, it is believed, it was not raised a few days later at the full Cabinet, last Tuesday.

Some 48 hours later at the EU summit, last Thursday, Jean-Claude Juncker, the European Commission President, raised the issue of extending the transition period and said it would afford both sides more time to agree a trade deal and so avoid the need for a backstop; he added it "probably will happen".

When the Scottish Secretary got wind of this possibility, he telephoned Downing Street and spoke to a top official, making clear his deep concern.

Any extension of the transition period would mean UK fishermen having to shadow the hated Common Fisheries Policy for another 12 months to at least December 2021; more than five years after the EU referendum. Scottish Conservative MPs have made clear they could not vote for any Brexit deal that did not contain an exemption for the fishing industry.

During Commons exchanges yesterday, the PM said that while she was not looking for a transition extension, she, nonetheless, admitted it might be a way to resolve the continuing impasse on the Irish border backstop. When pressed, she told MPs how the fishing industry was “right at the forefront of our thinking”.

Asked if the fishermen’s concerns were going to be properly looked at, her spokesman replied: “Yes, absolutely.”

Asked if the No 10 presentation had anything to do with concerns recently raised by Ruth Davidson, the Scottish Conservative leader, over maintaining the integrity of the Union, he said: “I would not put it in those terms, no. But there are obviously other parties involved in discussing matters relating to the Union.”

Asked if ministers held the presentation because they feared the Union was under particular threat because of Brexit, the spokesman replied: “Look, the answer on that is the PM has been clear throughout her approach in the Brexit negotiations, from day one up until now, on the importance of making sure it is a Brexit that delivers for each part of the United Kingdom; it’s absolutely her focus now and going forward.”

Asked if Mr Mundell had threatened to resign in relation to Brexit, he said: “No.”

Another Whitehall source stressed that the Cabinet's discussion on the Union had been earmarked well in advance and so was coincidental to any Brexit concerns.

It also emerged that Dominic Raab, the Brexit Secretary, who insisted “good progress” was being made in the talks with Brussels, would from now on give weekly updates to Cabinet colleagues.

“As we move towards exit day it makes good sense to ensure all ministers are fully informed of the full range of work that’s taking place in relation to both scenarios,” explained the spokesman. “The PM was very clear to stress that a deal was the most likely outcome and that was the outcome we want to achieve.”

He also said Donald Tusk, the European Council President, had made clear that he was prepared to call a special summit of the EU28 to seal a deal when there was “decisive progress”. The next scheduled European Council is on December 13 and 14.

But Mr Raab has insisted the UK Government wants a deal done by the end of November to allow time for the Commons to debate and have its “meaningful vote” on the Brexit deal.