EU boats would be denied access to UK waters after 2020 if European leaders refuse to sign a "fair agreement", Theresa May has said.

The Prime Minister responded to concerns raised by Scottish Tory MPs over fishing terms laid out in her Brexit deal. 

Mrs May refused to rule out Common Fisheries Policy rules being followed in an extended transition period but acknowledged such a move would be "unacceptable" to Scottish MPs. 

The Prime Minister's letter states: "In 2020 we will negotiate as a fully independent coastal state for fishing opportunities in 2021, as Norway does.

"If there is no fisheries agreement in place with the EU by then, of course, no EU country's fishing fleet will have access to our waters."

Read more: Brussels wants future deal to 'build on' existing EU fishing rights

The letter adds: "It has always been the EU's position that there should be a link between access to waters and access to markets as part of these arrangements - but they failed to achieve this in both the Political Declaration and the Withdrawal Agreement. It remains our resolute position that there should be no such link.

"If we cannot reach a new and fair agreement by the end of 2020 then the default position is that EU vessels would have no access to our waters, so they have a strong incentive to reach one."

The letter comes as a response to a joint letter from the Scottish Tories to the Prime Minister after she unveiled the draft Withdrawal Agreement to her cabinet two weeks ago.

All 13 Scottish Conversative MPs, including Scotland Secretary David Mundell, signed a joint letter detailing their fears over the fishing policy detailed in the draft Brexit agreement. 

HeraldScotland:

In the letter, the MPs warned: "We could not support an agreement with the EU that would prevent the UK from independently negotiating access and quota shares ... We also cannot stay in the Common Fisheries Policy after December 2020."

Read more: Scottish Tories threaten to vote down Brexit deal over fishing policy

Mr Mundell and Scottish Conservative leader Ruth Davidson, who is currently on maternity leave, both previously threatened resign over the proposed post-Brexit fishing policy. 

Today Mr Mundell faced fresh calls to step down, as SNP Cabinet Office spokesman Tommy Sheppard faced him in the Commons.

In wake of Mrs May's deal receiving cabinet backing, Nicola Sturgeon insisted Mr Mundell must quit if he is to retain “any last remaining scrap of principle or credibility”.