According to reports in the Daily Telegraph, the delayed exit from the policy was a ‘red line’ for both Mr Mundell and Ruth Davidson, with a letter from Mr Mundell being treated as a resignation threat by Cabinet ministers.
The latest warning comes days after Mr Mundell wrote to the Prime Minister saying that different treatment of Northern Ireland was an issue for himself and the Scottish Conservative Party.
In the correspondence from Mr Mundell, he warned that any special status for the EU would undermine the integrity of Brexit, and fuel independence calls in Scotland.
Speaking yesterday, David Mundell stated that any extension of Brexit negotiations would result in Britain staying in the Common Fisheries Policy, with many Scottish Conservatives stating that it is their “red line”
Theresa May yesterday said that she was willing to consider an extension “by a matter of months.”
From March 2019, the UK will be seen as “an independent coastal state” however, with a 21-month implementation period, the UK will need to wait until December 2020 before it can negotiate as a separate coastal state.
Leader of the Scottish Fisherman’s Federation, Bertie Armstrong, said that any extension was “unacceptable” and that any continuation of negotiations should not apply to fishing policy.
He said: “On Brexit day next year we will become a coastal state, but we have now, to our nanoyance, agreed to run on the rules of the CFP for an implementation period.
“That simply cannot be extended.”
He added: “Our biggest defence in all of this is our extremely strong line of irrefutable logic.
“In the words of the Scottish Government, £500 million and 5,000 jobs are at stake here.”
David Duguid, a Scottish Conservative Party MP for Banff and Buchan said that the CPF was hit red line and that 2019 should be the last time Britain sits at the CPF table as a member of the EU.
He said: “It’s my red line, it the Scottish Conservatives’ red line.
“The terms of the implementation period, which will be part of the withdrawal agreement, dictate how we manage fisheries in that period.
“The current position from Michale Gove as I understand is that we will be negotiating as an independent coastal state in December 2020.
Despite admitting that he was a “little alarmed” by current proceedings, he added that he remained confident the Conservatives would not forget the Scottish fisherman.
Michael Russell, Scotland’s Brexit Minister, said that the latest infighting from the Conservatives were “another humiliation from the Prime Minster” adding that “it is extraordinary that there is more unity among 27 EU nations than there is among the Prime Minister’s own cabinet.
Aberdeen South MP Ross Thomson said that in comparison, “no deal, which would give us immediate and total control of our waters and our money... is far more preferable”.