UK Government ministers could "give in" on fishing rights in key Brexit trade talks to win concessions for the financial services sector, a Holyrood committee has been told.

Charles Grant, the director of the Centre for European Reform, said a senior UK Government official had indicated the move.

Mr Grant said when it came to agreeing a deal with the EU, the other 27 nations "may not agree to any deal on anything unless the British give in on fish quite quickly".

His comments came less than 24 hours after Boris Johnson insisted Britain's fighing rights would not be "traded away" in the trade talks with Brussels.

During his People's PMQs broadcast on Facebook on Wednesday, the Prime Minister was asked if he could "guarantee" the UK would have full control of its fishing waters after Brexit.

“Yes, we will take back control of our fishing waters," declared Mr Johnson.

"We will ensure that we become an independence coastal state once again, having full jurisdiction over the 200-mile limit of our spectacular maritime wealth."

He then stressed: “We will make sure we don’t trade away Britain’s fishing rights as they were traded away for instance in the accession negotiations in the early 1970s. Be confident about fish.”

Mr Grant told the Scottish Parliament's Europe Committee: "I've heard a senior person in London, part of the Government, say we may have to give in on fish, we may have to give EU access to our waters or we won't get anything for the City of London.

"To be fair to him he didn't say 'we will sell Scottish fish to buy financial service access', it wasn't that brutal.

"He just said 'the kind of thing we may well have to do is to give access to EU boats in our waters otherwise we won't be able to get anything on financial services'.

"He was implying to me that he thought such a trade-off or bargain ... was at least something to be seriously considered and quite plausible."

Mr Grant said there was a "strong point of view in London that British fish can be sold to get a better deal on financial services".

He said the remaining 27 EU nations would negotiate strongly over fishing rights post-Brexit, describing it as a matter of "solidarity" for them.

"It's true only a third of the member states or less, fewer than that, care about fish, but this is a test of solidarity," he said.

"Even in some countries like Hungary that don't have fishing fleets, or Poland doesn't have much of a fishing fleet, they will feel the need to show solidarity with those like Denmark and Belgium and France and Spain who do care about fish."

The issue could be the "first and nastiest part" of negotiations with the EU over trade, he added.

He spoke after the committee heard that reaching an agreement with the rest of the European nations on issues such as trade before the end of 2020 - when the UK's Brexit transition period is due to finish - would be a "major challenge".

Fabian Zuleeg, the chief executive and chief economist at the European Policy Centre, said: "The European Union hasn't concluded a treaty like this within 11 months, even taking into account a lot of goodwill on both sides, which we can't guarantee, there are a lot of technical steps which have to be gone through.

"In my view it will be almost impossible to conclude."

With areas including aviation and security having to be considered, as well as trade, Mr Grant said if a deal could be reached it "will have to be very basic" and "many of the areas which are difficult will have to be postponed into the future".

He told the MSPs: "Something that is called a deal is possible by the end of the year so long as the UK accepts basically all the terms that the EU requires."