The UK Government is planning to withhold power from Scotland and Wales when the Brexit transition ends, according to reports.

The Financial Times reports a 'state aid proposal' is expected to appear in a bill this autumn which would give Westminster statutory powers to control policies for the entire UK. 

The potential legislation could see state aid policies for all evolved nations controlled solely by Westminster.

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Scotland's First Minister Nicola Sturgeon has said this would be 'a full-scale assault on devolution'.

She tweeted on Monday morning: "Make no mistake, this would be a full-scale assault on devolution - a blatant move to erode the powers of the Scottish Parliament in key areas.

"If the Tories want to further boost support for independence, this is the way to do it."

FT reports the legislation would enable Westminster to force both Scotland and Wales to accept whatever new standards regarding food, environment and animal welfare it agrees in future discussions and agreements with other countries.

The transition period ends on December 31, and state aid remains to be one of the most contentious issues in UK negotiations with the EU.

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The governments in Scotland and Wales have said that this policy should be devolved to them, however, the UK government insists it should be down to them.

Scotland's Constitution Secretary Mike Russell has previously said plans to enshrine a UK "internal market" after Brexit would seriously undermine devolution, describing them as a potential "power grab".

In a letter to Cabinet Office minister Michael Gove, Mr Russell said he is concerned about proposals for an external body that would "test" whether a bill in Holyrood affected the UK's internal market and plans for a "mutual recognition regime", which he said could lower regulatory standards beyond what the Scottish Parliament found acceptable.

In response, Mr Gove accused him of trying to "confect" a political row.

Commenting, SNP Westminster Leader Ian Blackford MP said: "Boris Johnson's outrageous plan for a power grab on the Scottish Parliament is another shameless Tory attack on devolution - and we will resist it every step of the way.

"Yet again, Scotland is being completely ignored by Westminster. If the Tory government goes ahead with this attempt to roll-back devolution they will drive support for independence up even further.

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"Westminster has proved itself to be utterly incapable of acting in Scotland's interests. With the exception of the Scottish Tories, who have completely isolated themselves, the Scottish Parliament is united against moves to erode Scotland's devolution settlement.

"It's time for Jackson Carlaw to come out of hiding, find a backbone, and join the SNP in opposing this completely unacceptable move. Otherwise he will prove the Scottish Tories only exist to do Boris Johnson's bidding - however damaging.

"Scotland has been ignored throughout the Brexit process, shut out of the trade negotiations, and now our interests are being bulldozed for a Tory-Trump deal. It is clearer than ever that the only way to protect Scotland's interests and our place at the heart of Europe is to become an independent country."