NICOLA Sturgeon has dramatically ramped up her rhetoric over a second referendum, accusing the UK Government of using Brexit to attack “the very foundations” of devolution.

In a fiery speech, the First Minister told an academic audience that powerful forces at Westminster were trying to exploit Brexit to “rein in” Holyrood.

She warned Scotland and the UK face a constitutional “crossroads moment” because of Brexit , in a clear hint a second independence referendum is approaching.

Ms Sturgeon claimed Scots faced a choice about what kind of country they wanted, copying a Tory post-Brexit Britain or heading in a more enlightened direction.

She has already said a referendum is “very likely” in light of Brexit, and “all but inevitable” if Theresa May rejects her plan to keep Scotland in the European Union single market.

However with the Prime Minister due to trigger the Article 50 withdrawal process later this month, there is little sign the UK Government has any appetite for such a deal.

Addressing the David Hume Institute in Edinburgh, she claimed that, after almost 20 years of progress, devolution was facing “a grave threat” from Conservative MPs and ministers.

She said this “harm to Scotland’s interests” and identity made an independence referendum “almost a necessary way of giving the people of Scotland a say in our own future direction”, she said.

She said: “As a result of the Brexit vote, we, Scotland and the UK, stand now at a crossroads.

“Decisions taken in the months to come will reshape our economy, our society and our place in the world. In short, they will reshape the kind of country we’re going to be.

“The question is: should we decide for ourselves which path to take, or are we willing to have that path decided for us?

“We may all offer different answers to that question, but surely the choice should be ours.”

She attacked the UK Government for undermining “the very foundations” of devolution by refusing to guarantee powers in devolved areas such as farming and agriculture would be fully repatriated under Brexit, saying the Tories wanted to “strip” Holyrood of its rightful powers.

She said: “That would would be unacceptable. It would betray the claims and the basis of the existing devolution settlement.”

In a later question and answer session, Ms Sturgeon said: “The UK is heading down a very different path to the one that was envisaged in 2014. The question for me is, should Scotland simply be taken down that path by default, regardless of what our views are, or from a democratic point of principle should we get a choice? That’s one of the things that weighs in my mind about the democratic choice that perhaps, if things develop as they appear to be, that maybe Scotland has a right to make, and it would then of course be Scotland’s choice. If we are in that scenario, I wouldn’t be intending to lose.”

On the possible timescale for a second referendum, she said: “We want to be in a timescale where our options don’t get closed down, where we have the ability to fashion our own relationship with the EU without having a situation where we ended up diverging hugely. The outlines of that [Brexit] agreement for the UK really need to emerge by the autumn of next year in order to go through the ratification process. That, hopefully, is a time when we do start to have more clarity. Obviously there are bigger issues in determining what’s right for Scotland in the next step.”

But she conspicuously failed to say whether rejoining the EU would be part of the SNP’s offer if there was a second referendum, saying only that if there was a vote, she would be clear about choices on Europe, the currency and economy at the time.

She said the Scottish Government had declined to join a legal action to determine whether Article 50 was irrevocable or could be abandoned.

Scottish Secretary David Mundell told MSPs last week: “There will be no taking back of any powers that are currently exercised here in the Scottish Parliament or, indeed, the Welsh Assembly or the Northern Ireland Executive. We are absolutely clear in relation to that.”

Scottish Tory leader Ruth Davidson said: “This hyperbole from the First Minister takes synthetic grievance to a whole new level. Frankly, she sounds shrill. Nicola Sturgeon’s attempt to use Brexit to manufacture the case for a second referendum has quite simply failed. She should now take it off the table so Scotland and the UK can work to get the best Brexit deal possible.”

Scottish Labour leader Kezia Dugdale accused Ms Sturgeon of “ridiculous scaremongering”.

A UK Government spokesman said: “These claims completely misrepresent our position. We have been very clear that no decisions currently taken by Holyrood will be taken away.”