IN a stinging rebuke Theresa May has been accused of adopting an insulting and condescending approach to Scotland after the Prime Minister demanded "a new grown-up relationship" with SNP ministers on the eve of a face-to-face showdown with Nicola Sturgeon.

Former First Minister Alex Salmond savaged the Tory leader ahead of her crunch Brexit talks with his successor in London tomorrow, describing Cabinet ministers around her as "planks of wood", after senior Tories like Brexit Secretary David Davis ruled out a Scottish EU deal over areas like immigration in the event of a hard Brexit.

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He said May's intervention was insulting to Scots and was "telling off" Sturgeon's ministers by suggesting the SNP administration had taken a childish approach to its Westminster counterpart.

May also risked further inflaming tensions with Sturgeon ahead of tomorrow's talks, as the Tory leader restated her commitment to "our great Union".

Downing Street said the Prime Minister will set out her vision for a new way of working between the UK Government and the devolved administrations at her first Joint Ministerial Committee tomorrow.

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She will call on the devolved administrations to commit to fully working with the UK Government to boost the prosperity and security of the people of England, Scotland, Wales and Northern Ireland.

May met Sturgeon at the First Minister's official Bute House residence in Edinburgh soon after she succeeded David Cameron in July, although tomorrow will be the first substantial policy talks between the pair.

Speaking ahead of the meeting, May said: “When I stood upon the steps of Downing Street I made clear the importance of our great Union.

“Far more than mere geography brings us together – and we are much more than the sum of our parts. As we move into this new chapter, we must seize the opportunities ahead, as we will achieve far more together than we could ever do apart.

“I want Monday’s meeting to be the start of a new grown-up relationship between the devolved administrations and the UK Government – one in which we all work together to forge the future for everyone in the United Kingdom."

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In response Salmond blasted May's remarks, which he suggested were condescending to Scots.

In an exclusive interview with the Sunday Herald, the SNP's international affairs and Europe spokesman at Westminster, said: "The Prime Minister is struggling very badly and her policy on Europe is increasingly becoming a shambles.

"With her talk about a grown-up relationship, she needs to understand that she can't scold Scottish Government ministers in the way she scolds her own departmental ministers.

"She should not assume that the Scottish Government is in the same state of confusion as her own government over Europe."

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He added: "Theresa May should start looking at some of the planks of wood in her government. Planks of wood would be a good description of some members of her government.

"Theresa May's schoolmarm tone of telling people off who disagree with her is no way to run a government and is certainly no way to speak to members of the Scottish Government."

Salmond said that May's intervention would rally support for a second independence referendum, which Sturgeon's administration published draft legislation for last week.

The First Minister has suggested that Scots should have the ability to reconsider the issue in light of the Brexit vote.

She also told the SNP conference she would call a new referendum if Scotland was pulled out of the single market against its will.

Salmond, the SNP MP for Gordon, hit out at a claim from Downing Street made last week that Sturgeon did not have a mandate for a second independence referendum.

He said: "The statement from Theresa May's spokesperson last week that Nicola Sturgeon does not have a mandate is one of the most absurd I've ever heard in politics as it comes from a Prime Minister not elected by the public about a Scottish First Minister was overwhelmingly re-elected this year."

"For a Prime Minister with a non-existent mandate it's no way to treat a government that has a mandate."

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Sturgeon has said the Scottish Government would unveil proposals in the coming weeks for new powers to help Scotland retain free movement of goods and services in the EU, even if the rest of the UK leaves.

Commenting on the move, Salmond added: "Unless Theresa May is prepared to listen and to accept the plan that Nicola Sturgeon is putting forward there will be another independence referendum in about two years' time. If I was Theresa May I'd tell my ministers to listen more to Scotland.

"May has had the shortest honeymoon in political history and her latest comments will go down like a lead balloon in Scotland. They will rally support for the proposals Nicola Sturgeon puts forward.

"The Prime Minister should listen very carefully to the proposals by Nicola Sturgeon over the red-line issues like the single market, migration, the treatment of European citizens and the protection of social and employment rights for Scottish workers."

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Another former First Minister, Labour's Henry McLeish, said that the approach of "cheap patriots" and anti-EU fanatics in May's Cabinet could lead to a vote for independence if a second referendum was to be called.

He said: "The greatest threat to Scotland's place in the Union is from those in the Tory Party with their utter contempt for Scotland's vote to Remain. Theresa May's failure to wake up this crisis risks the break up of Britain."

Sturgeon's lead minister involved in the process demanded that Scotland is treated as an "equal partner" by May in the negotiations.

Michael Russell, the minister for UK negotiations on Scotland's place in Europe, said: "The Scottish Government is becoming increasingly concerned that the UK is heading for a hard Brexit with all the damage that will bring to the Scottish and UK economies.

"The Prime Minister has set the clock ticking and the UK Government must use the time before triggering Article 50 to engage properly with all the devolved administrations and show that they are willing and able to treat Scotland as an equal partner."

However, Scottish Labour leader Kezia Dugdale called on Sturgeon to negotiate on behalf of "all the people of Scotland, not just the minority of people who support Scottish independence".

In a letter to the First Minister, Dugdale said: "As the First Minister of Scotland, Nicola Sturgeon is negotiating on behalf of people throughout Scotland. That should be at the forefront of her mind throughout the Brexit negotiations. That means she must speak for all the people of Scotland, not just the minority of people who support Scottish independence."