Fergus Ewing told MSPs today that the Tories are "unravelling" on the fishing issue, after it emerged that a two-year "transition deal" after Brexit will keep the Scots fleet in the Common Fisheries Policy. This allows fleets from across the EU to access Scotland's rich waters and has provoked fury among fishing leaders, as well as Scots Tory MPs.
But Mr Ewing indicated that this is just the beginning and suggested during a Holyrood question and answer session that the UK Government is preparing to "trade away" access to Scottish waters in the final Brexit deal.
Ms Davidson issued a joint statement with Environment secretary Michael Gove setting out a Uk Government promise to leave the Common Fisheries Policy as of Match 2019.
"It's outrageous that Ruth Davidson and Michael Gove could have issued such a misleading statement last weekend when they must have know what was about to happen.
"The only thing that is clear now is that Ruth Davidson's credibility lies in ruins.
"She must apoologise for her broken promise to our fishing industry."
The transition deal is the "worst possible outcome", Mr Ewing added, as it means the UK will be in the CFP not as a partner at the table, but "at best consulted with."
But he added: "We will become a independent coastal state - it is happening. The SNP has been against Brexit from the start - they would gladly rejoin the EU in a heartbeat."
Current SNP policy is to rejoin the EU and the "hated CFP" Mr Ewing added.
The Cabinet Secretary insisted that the SNP had "nothing to regret or apologise for."
He added: "What we're witnessing is a complete betrayal by the Conservative party, of the policies that were made - incidentally persuading people to vote for Brexit in the first place.
"Now we see these promises are gradually unravelling. The first to unravel is the date. The next I suspect will be the substance.
"I have asked Andrew Leadsom, Michael Gove and George Eustace face to face and over the table in discusssions time and time again: Will you give an unequivocal assurance that the UK Government will not trade away permanent access to our exclusive economic zone, our fishing rights, as part of Brexit deal.
"I have had no answer to that questions whatsoever."