NICOLA Sturgeon has warned that Theresa May's post-Brexit power deal would "completely demolish" Scottish devolution.

Writing exclusively in today's Sunday Herald, Sturgeon forecast a bleak future for the Scottish Parliament in post-Brexit Britain.

The First Minister's stark warning came ahead of planned talks this week between Scottish and UK ministers.

READ MORE: 'Be under no illusions, the Tories will demolish Scottish devolution'- Nicola Sturgeon writes for the Sunday Herald

After the transfer of powers from Brussels to Whitehall and Westminster, London plans to take charge of policy areas traditionally devolved to Holyrood for seven years.

Sturgeon said that means "completely demolishing the principle at the heart of the devolution settlement" by giving Westminster the final say on many devolved policy areas.

She warned that May's Brexit powers deal would leave Conservatives free to rip up flagship Scottish Parliament legislation.

Sturgeon warned that a right wing government led by an arch-Brexiteer such as Jacob Rees-Mogg would "trample all over" the "gains of devolution".

READ MORE: 'Be under no illusions, the Tories will demolish Scottish devolution'- Nicola Sturgeon writes for the Sunday Herald

Laws passed by MSPs such as a GM crops ban and minimum pricing for alcohol would be put at risk by a "Tory power grab", she claimed.

Sturgeon also warned that the Scottish NHS and the country's "more humane welfare system" would also come under attack.

Scotland would also be at the mercy of any UK trade deal with US President Donald Trump, Sturgeon said, which she warned would "see us subjected to chlorinated chicken and hormone-injected beef".

The UK wants to retain control over 24 devolved areas, mostly related to agriculture, fisheries and the environment, for up to seven years in order to provide UK-wide stability.

READ MORE: 'Be under no illusions, the Tories will demolish Scottish devolution'- Nicola Sturgeon writes for the Sunday Herald

However, Sturgeon says those terms would see Westminster "hold the whip hand" over devolved powers, adding: "If our principled stance means the SNP are the only or the last party standing, defending the founding principles of devolution, then so be it."

In a dramatic raising of the stakes, Sturgeon challenged Labour to back her. The Labour government in Wales accepted a compromise last week.

Sturgeon said: "For Labour, the challenge is whether they are prepared to defend those founding principles of devolution, championed by Donald Dewar and backed by the people in a referendum, or alternatively are prepared to roll over and accept a Tory power grab."

READ MORE: 'Be under no illusions, the Tories will demolish Scottish devolution'- Nicola Sturgeon writes for the Sunday Herald

Sturgeon added: "After Brexit, the UK Government has made clear it wants the final say on many devolved policy areas which are currently subject to EU law – completely demolishing the principle at the heart of the devolution settlement endorsed democratically by the people of Scotland more than 20 years ago."

Sturgeon also accused the Conservatives of twisting language out of all recognition, saying: "They say that Westminster would not seek to legislate in devolved areas post-Brexit unless the issue had been subject to a so-called “consent decision” by the Scottish Parliament.

"But the Conservatives then go on to give their own very particular definition of a consent motion. It is, they say, when the Scottish Parliament has voted in favour of a motion consenting to what is proposed. Or when it has voted against such a motion. Or indeed when Holyrood decides not to lay and vote on a motion at all.

"So if the Scottish Parliament says yes, it is taken as agreement, if it says no it is similarly taken as agreement – and if it does nothing at all, that too is agreement in the language of post-Brexit Toryism. It is as surreal and perverse a definition of the word consent possibly ever to have been concocted in the English language."

Sturgeon has already dismissed the UK Government's last offer on the EU Withdrawal Bill, which she claimed would still allow Westminster to override the will of Holyrood and impose legislation.

However, her latest intervention represents a hardening of the battle lines with Westminster ahead of crunch talks with Tory ministers in London, pencilled in for Wednesday.

Scotland's Brexit minister Mike Russell is to meet UK cabinet office minister David Lidington and Scottish Secretary David Mundell, as part of the Joint Ministerial Committee.

Sturgeon warned that the Tory deal would erode the Scottish Parliament's status in "unforeseeable ways", adding: "We should be under no illusions about how extensive that power grab could be – the Tory proposal would see Westminster hold the whip hand over devolved powers for a period of seven years."

However, a UK Government spokesman said: "The agreement we have reached with the Welsh Government will provide legal certainty and increase the powers of the devolved legislatures. We hope that the Scottish Government will now sign up to this sensible, pragmatic compromise."

Meanwhile, Labour MSP Neil Findlay defended the Welsh government's decision to accept a compromise arrangement.

Findlay said: "The Welsh Government are as committed to protecting devolution and their right to provide consent to anything impacting on Wales as the Scottish Government are. Both the Scottish and UK governments must get back around the table, end the political posturing and work constructively and in good faith to bring about a deal."