NICOLA Sturgeon will not budge in her opposition to the UK Government’s Brexit Bill as her power struggle with Theresa May pushes the country towards a constitutional crisis.

The SNP leader is adamant that “no First Minister worth their salt” would agree to the Prime Minister’s terms, which she claims amount to a power-grab by Whitehall and has insisted that securing for Holyrood all 111 powers and responsibilities coming from Brussels post Brexit is an “issue of principle I won’t compromise on”.

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Ahead of a PM-FM showdown on Brexit on March 14, the constitutional battle is set to continue today when Mrs May makes a Commons statement on her Mansion House speech and Michael Russell, the Scottish Government’s Brexit Minister, gives evidence to the Commons Constitutional Affairs Committee in Edinburgh.

On Thursday, Mr Russell will have more talks with David Lidington, Mrs May’s de facto deputy, at a Joint Ministerial Committee meeting, to try to break the constitutional deadlock but Conservative backbencher Stephen Kerr, while hopeful of a resolution, suggested that no deal would be agreed before the PM-FM meeting on March 14.

“Nicola will want to go to London and claim victory before the TV cameras,” declared the MP for Stirling. “People tell me they want us to work together to get things resolved but there is an underlying suspicion that it serves the SNP leadership’s political purposes if they continue to be obstinate.”

His Tory colleague, Andrew Bowie said the blame for the continuing row over the flagship EU Withdrawal Bill was “firmly at the Scottish Government’s door”.

“The UK Government has changed its approach and has been conciliatory. I’m not sure what more it can do. Personally, I and others are fed up with the SNP Government and feel we have been taken for a ride from the beginning,” said the West Aberdeenshire and Kincardine MP.

Whitehall has changed tack and agreed the “vast majority” of the 111 powers and responsibilities should now go directly to Holyrood following Brexit Day but it wants to hold back 25 covering issues such as agriculture, fisheries and environmental protection so that common frameworks can be agreed to avoid any damage to the UK’s internal market.

However, Ms Sturgeon insists the principle of the devolution settlement is under threat, telling ITV’s Peston on Sunday: “There is an issue of principle at stake that we won't compromise on because if we did we would allow Westminster to exercise a power-grab on the responsibilities of the Scottish Parliament and I don't think any First Minister worth their salt should agree to that.”

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Mrs May, whose speech on Friday succeeded in getting a qualified welcome from most Remainers and Brexiters in her party, insisted she had set out an “ambitious”, “credible” and “practical” vision for Britain outwith the bloc, in which it would align with EU rules to get "frictionless" trade but would retain the freedom to diverge.

Downing Street and Boris Johnson denied Gavin Barwell, the PM’s Chief of Staff, was behind a leak of the Foreign Secretary's private thoughts on the contentious issue of the Irish border, which is proving to be the biggest hurdle in the Brexit negotiations.

On Friday, Mrs May rejected "unacceptable" EU proposals to retain customs union arrangements in Northern Ireland but acknowledged the UK's "responsibility" to help maintain a soft border with the Republic, spelling out in detail how she believed this could be achieved by technological means or through a broader trade agreement.

Yet, Simon Coveney, the Irish foreign minister, cautioned that he was "not sure the EU will be able to support" her plan as it would be worried about protecting the integrity of single market.

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Elsewhere, the PM’s Brexit address appeared to have given potential Tory rebels pause for thought; they had been threatening to side with Labour in favour of a customs union in the forthcoming Trade Bill.

One, senior Tory Sarah Wollaston, stressed she and others would now give the PM "breathing space" to try to negotiate her own customs plan, saying: “What we need to see is some kind of partnership that allows frictionless trade at our border and also deals with the situation in Northern Ireland and I want to give her the space to do that."