A new constitutional settlement between Edinburgh and London will be needed should Brexit take place, Michael Russell will say today.

The Scottish Government’s Constitutional Relations Secretary in a speech in London to an audience of government officials, business leaders and academics follows a declaration from Nicola Sturgeon that Theresa May is now effectively “out of power” and has no way forward on Brexit.

In a speech to the Institute for Government think-tank in London, Mr Russell will say: “Brexit has proved too heavy for devolution to bear and therefore a new constitutional settlement will be required should Brexit take place.

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“The first task we should all have is to ensure that the Brexit process is halted, temporarily or permanently. It is, therefore, obvious Article 50 must be extended and our preference is for that extension to be one that would allow a further referendum on EU membership with Remain on the ballot paper.”

Failing that, the Scottish Government minister will argue, Article 50 should be revoked before the UK leaves the EU to prevent a no-deal outcome.

“Only these steps can give us a chance of escaping from the disasters of Brexit with some semblance of order,” Mr Russell will declare.

He will add: “Then we must take the necessary steps to create a new constitutional settlement for these islands. For Scotland that means establishing a new relationship based on equality and only independence for Scotland can do that.”

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After taking part in the People’s Vote rally in London at the weekend, when an estimated one million people demonstrated for a second EU poll, the First Minister commented on the Brexit crisis gripping the Conservative administration.

“If we were in any normal period in British politics, she[the Prime Minister] would be long gone but the conventional rules are not applying.

"I suppose the one caveat to that is she is effectively out of power now and perhaps debating her position is becoming more and more incidental by the day.

"The Government has absolutely failed to deliver on the result of the 2016 referendum. They have no credible way forward now and when Parliament and Government fails, then it seems to me the only sensible thing to do is put the people back in charge," she told BBC 1’s Andrew Marr Show.

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Ms Sturgeon stressed the SNP's first choice was for Scotland and the UK to remain in the EU rather than having a "soft" Brexit and the best way of achieving that was to have another referendum or to revoke Article 50.

"At the moment, it's fair to say that the option of remaining is not off the table and it's not beyond the realms of possibility by any stretch of imagination. So as long as our first preference remains an option, that is what the SNP will back," she explained.

The FM insisted the case for independence had been bolstered by events of the past three years but when quizzed about any formal announcement to call for another Scottish referendum remained uncommitted.

She told the Marr Show: "Scottish independence referendum is going to happen. Nothing in this life is absolutely inevitable, but it's as inevitable as it's possible to be.

"Before I set a path forward for Scotland, it's reasonable for me to know what the starting point of that journey is going to be and the context in which we are going to be embarking on it.

"We need to know -and hopefully we will know this over the next few days and the next three weeks - is the UK leaving the EU? Is it leaving with a deal? Is it leaving with no-deal or is it not leaving at all? Perhaps looking at another referendum.”

Ms Sturgeon added: "But the experience of the last almost three years now - Scotland's vote ignored, the voice of the Scottish Parliament ignored, all of the consequences that flow from Brexit completely outwith our control;- that really does make the case for independence very, very powerfully."