Devolution is being “hollowed out” by Boris Johnson, who secretly wants to take back powers from devolved parliaments, John Swinney will claim.
Scotland’s Deputy First Minister will tell the SNP conference to “stand up and be counted before it’s too late” to defend devolution.
Mr Swinney is expected to tell members that the Conservative Government wants “unfettered Westminster control on Scotland” and is using Brexit to undermine devolution.
But his comments have been dismissed as “simply nonsense” by the UK Government.
In a virtual speech, he will argue that “the only way to keep the gains of devolution is by becoming independent” and suggest that decisions made at Holyrood “can be routinely undermined at a whim by the Tories”.
Mr Swinney is expected to say: “We are now seeing a concerted attack on our parliament, from the very people who fought tooth and nail against it being established in the first place.
“In a grotesque irony, the Tories are using something that the people of Scotland voted overwhelmingly against – Brexit – to undermine something they voted overwhelmingly for – the Scottish Parliament.
“Through the Internal Market Act, the Tories have given themselves unfettered power to decide the rules of the internal market – and to completely ignore the devolution settlement if they want to.”
Claiming that the Prime Minister could wish to reverse devolution, Mr Swinney will add: “There will be no sudden Big Bang moment, Boris Johnson is not going to stand up and announce to the cheering Tory faithful that he is dismantling the devolution settlement – much as I am sure he would like to.
“But make no mistake – piece by piece, devolution is quietly being filleted, hollowed out from the inside by a Tory Party which has always opposed the idea of anything other than unfettered Westminster control on Scotland.
“Much like the climate emergency, which is slowly creeping up on us every single day – we need to issue a code red for devolution.
“All of us who care so deeply about the Scottish Parliament and its role in Scottish public life need to stand up and be counted before it is too late.”
A UK Government spokeswoman said: “This is simply nonsense.
“The Internal Market Bill ensures that vital trade can continue seamlessly between all four corners of the UK.
“Now more than ever, people in Scotland want to see the UK and Scottish governments working together to protect lives and livelihoods.
“The pandemic, and our collective response – from the furlough scheme to vaccine procurement and the backing of our military personnel – has shown that we are at our strongest when we work together.”