THE First Minister has again insisted that Scotland should be given the “same opportunity” as Northern Ireland to stay in Europe’s single market post-Brexit.

Nicola Sturgeon warned that without such an arrangement being in place, Scotland would be left competing for investment with a country which was “effectively” still part of the trading bloc.

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Her message, echoed by SNP Westminster leader Ian Blackford, came as Theresa May prepared to face her Cabinet in a showdown meeting over the draft Brexit deal.

Sturgeon said on Twitter that the “PM’s approach would take Scotland out of the single market (despite our 62% remain vote) but leave us competing for investment with Northern Ireland that is effectively still in it”.

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Her remarks came as DUP chief whip Sir Jeffrey Donaldson said the arrangements for Northern Ireland could lead to the break-up of the United Kingdom.

He claimed the deal would in the “long term” leave Northern Ireland closely aligned with the EU and could increase support for Scottish independence.

“It’s about the constitutional and economic integrity of the UK, that is fundamental for us,” he said.

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He added: “The DUP does not stand alone on this, we have many friends within the Conservative Party, and indeed in some other parties, who believe this deal has the potential to lead to the break-up of the UK.”

Scottish Conservative leader Ruth Davidson, who is currently on maternity leave after the birth of her son, and Scottish Secretary David Mundell have both warned they could quit their roles if Brexit threatens to “undermine the integrity” of the UK.

SNP MP Blackford said the two Tories had “got questions to ask”, but added: “I’ll leave that to them.”

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He stressed that Scotland should be treated the same as Northern Ireland.

“As far as we understand things this morning it looks as if it’s actually going to a be a different deal for Northern Ireland,” he said in a radio interview.

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“If it’s permissible for Northern Ireland to stay in the single market as part of the backstop – and I welcome that for the people of Northern Ireland – then of course Scotland should be given the same opportunity.”

He continued: “Nicola Sturgeon, our First Minister, has been very clear ever since the Brexit vote that we need to respect the votes of the people of Scotland and as a very minimum that means staying in the single market and the customs union, these are our red lines.”

Blackford insisted it was “absolutely right” that the Brexit deal should enshrine the Good Friday agreement, which ended years of conflict in Northern Ireland, and ensure there is no return to a hard border with the Irish Republic.

But he went on: “The key point is that if there is to be a differentiation for Northern Ireland there is no reason why the circumstances in Scotland cannot also be respected.

“We need to stay in the single market and the customs union, and the Government in London must listen to us on that.”

Blackford pressed May on a special deal for Scotland at Prime Minister’s Questions and quizzed her on whether the meaningful vote in Westminster on the Brexit deal could be amended. May does not want to allow amendments to the motion, which could lead to MPs voting on whether to hold a second EU referendum or People’s Vote.

There was also anger yesterday when it emerged the Chief Minister of Gibraltar had seen details of the agreement between the UK and EU, while the Scottish Government did not. In the Commons, the SNP’s Kirsty Blackman said Fabian Picardo had “been briefed by the Minister of State for Europe”. “I understand that no such courtesy has been afforded to the Scottish Government,” she added. The Aberdeen North MP asked why ministers in Edinburgh had not yet seen the final deal, while Gibraltar had.

David Lidington, May’s deputy, said he had already had a “very constructive meeting” with the first ministers of Wales and Scotland last Friday morning.

He added: “The Prime Minister will, when the cabinet has taken a view and come to a decision about what has been agreed provisionally between negotiators, talk directly to the First Ministers of Scotland and Wales, because it is quite right that they should be fully briefed on what it is that the cabinet has decided.”

Sturgeon also hit out at the failure of the PM to speak to her before the emergency Cabinet meeting yesterday so Scottish Government concerns could be fed into the meeting.

She tweeted: “The PM has offered to call me after her Cabinet meeting – I have suggested that we should speak ahead of the meeting so that @scotgov concerns about what is emerging can be relayed to the Cabinet BEFORE they take a decision. She has so far refused. The “respect” agenda in action.”