A political battle over Brexit and fishing rights took place at Holyrood and at Westminster with Nicola Sturgeon accusing Theresa May of “selling out” Scotland’s fishermen.

The Prime Minister insisted that, post the transition period in December 2020, Britain would become an “independent coastal state” and claimed if anything was a sell-out, it was the SNP’s policy to keep Scotland in the hated Common Fisheries Policy.

The bitter row broke out after the UK and EU27 agreed a text on their future relationship post Brexit, which is due to be signed off at a special summit in Brussels on Sunday.

It states: “Within the context of the overall economic partnership, the parties should establish a new fisheries agreement on, inter alia, access to waters and quota shares.

“The parties will use their best endeavours to conclude and ratify their new fisheries agreement by July 1 2020 in order for it to be in place in time to be used for determining fishing opportunities for the first year after the transition period.”

The SNP leadership smelt a rat and accused UK ministers of preparing to use Scottish fishermen as a “bargaining chip” as it fears countries like France and Spain will use the future trade talks to get continued full access to UK waters following withdrawal; something Whitehall insists it will not allow to happen.

At First Minister Questions, Ms Sturgeon said: "The political declaration that has been agreed between the UK Government and the European Commission this morning represents another Tory sell-out of Scottish fishermen.

"What we see is that the Scottish fishing industry will be used as a bargaining chip in wider trade talks," she declared.

The FM recalled how last week all 13 Scottish Conservative MPs sent a letter to Mrs May, making clear post Brexit the UK "must be able to negotiate access and quota shares on an annual basis without any pre-existing arrangement being in force" and "this means that access and quota shares cannot be included in the future economic partnership".

But she noted the text of the agreement made no mention of annual negotiations, which, she told MSPs, “I happen to know the UK Government was trying to secure and they failed”.

Ms Sturgeon added: "In terms of David Mundell's position I would simply say this: his position is a matter for him but if he is still in office by the end of today in light of this political declaration he will have forfeited forever any last remaining scrap of principle or credibility that he had."

Labour's Lesley Laird, the Shadow Scottish Secretary, echoed the call for the Scottish Secretary to "resign with immediate effect".

But the Cabinet Minister hit back, tweeting that he would “not take lessons on standing up for fisherman from Nicola Sturgeon, who is committed to trapping them in the hated Common Fisheries Policy”.

He added: “The PM has fiercely resisted the efforts of EU states to make an explicit link between access to our waters and access to markets. We will negotiate and decide, as an independent coastal state, on access and quota[s] on an annual basis, just like Norway and Iceland do now.”

However, his Scottish Conservative colleague, Ross Thomson, referred to the text’s reference to a new fisheries agreement on access to waters and quota shares, saying: “This means sovereignty over our waters sacrificed for a trade deal."

At Westminster, Ian Blackford took up the SNP’s attack, telling MPs Scotland's fishing rights had been "thrown overboard as if they were discarded fish".

The Nationalist leader told Mrs May she had just lost the votes of her Scottish Tory colleagues, who could “not possibly vote in favour of this sell-out of Scottish fishing interests".

But the PM hit back, insisting the UK would become an "independent coastal state with control over our waters" before saying to Mr Blackford: "I will tell him what a sell-out of Scottish fishermen would be: it's the policy of the Scottish National Party to stay in the Common Fisheries Policy."

Meanwhile, Bertie Armstrong of the Scottish Fishermen’s Federation, said: “We will continue to seek assurances from the UK Government that it will remain steadfast and will not rest until the future arrangements are signed, sealed and delivered, and we secure that critical control over access to our waters and who catches what stocks, where and when.”