And the First Minister stepped up calls for a People’s Vote on remaining in the EU as Mrs May’s hopes of getting her deal through Parliament nosedived after Speaker John Bercow ruled out a third vote without substantial changes.
The SNP leader has hit out at speculation the Democratic Unionist Party (DUP) may be allowed a seat at Brexit trade talks in an effort by Mrs May to secure the passage of her deal in Parliament and avoid an extension to Article 50.
The Prime Minister has been urged to provide greater clarity and assurances following reports of the concessions she was prepared to offer the DUP to win a majority to pass her Brexit deal.
It came before Mr Bercow yesterday dealt a damaging blow to the prospect of a third meaningful vote being brought before Parliament when he ruled this out without there being substantial changes to the motion.
Ms Sturgeon’s letter stated: “Since the EU referendum in 2016 there has been sustained and consistent damage done to the devolution settlement, and to the idea that the UK is a partnership of equal nations.
“In the past two years however, Scotland’s wishes and national interests have been roundly ignored and at times treated with contempt by the UK government.”
Scotland and Northern Ireland both voted by a majority to remain in the EU in the 2016 referendum, but the weight of votes in England and Wales swung the outcome in favour of Leave.
Ms Sturgeon said she has “three major concerns” over the Prime Minister’s reported strategy, including the prospect of the DUP being represented in talks on the future trade relationship between the UK and EU when the Scottish Government has been excluded. The Scottish Government published a paper last August calling for its role in international trade negotiations to be respected.
Ms Sturgeon’s letter adds: “There has been no indication that the UK government is taking these proposals seriously, although there has since been support for a greater role for devolved administrations in trade negotiations from both the International Trade and Scottish affairs select committees in the House of Commons.
“In addition, there have been no meaningful moves to ensure the devolved governments have a properly enhanced role in the next phase of EU-UK negotiations.”
The UK government’s proposals to the DUP also appear to mean “a serious curtailment of the powers of the Scottish Parliament”, according to the SNP leader.
The letter added: “Many of the relevant rules fall within devolved competence and therefore it is not in the gift of the UK government to unilaterally constrain the powers of the Scottish Parliament in order to strike a deal with the DUP. Continued alignment can only be guaranteed with the full support of the Scottish Government and Parliament.
“As you will be aware, the Scottish Government continues to be concerned that Scotland will be placed at a disadvantage if your proposals take effect.”
Scotland has lost out to the tune of £3.3 billion, Ms Sturgeon claimed, of equivalent funding after more than £1 billion was given to Northern Ireland in a bid to win DUP co-operation.
Ms Sturgeon said in the letter: “I have said and will continue to say that while there is no broad consensus in the UK Parliament for your Brexit deal, the decision ought to be put back to the people in a second EU referendum – that is the responsible and democratic thing to do.”
But she added: “Should the UK continue on a path to exiting the EU, then there must be fair and equal treatment of the four nations of the UK in relation to influence over and a role in the negotiations of the future relationship through the properly constituted devolved institutions.
“At present, far from ensuring such fair treatment you appear to be pursuing a path that privileges one political party, further constrains the powers of the Scottish Parliament and short-changes public spending in Scotland. This approach would not be acceptable.”