NICOLA Sturgeon has warned Boris Johnson's plans to seize control of state aid would represent a “full-scale attack on devolution”.

Tory ministers are preparing to table legislation which would give Westminster statutory powers to control policies for the entire UK.

State aid policies – such as subsidising companies – are among the powers currently controlled by the EU, but which Holyrood expects to oversee after Brexit. However, Boris Johnson’s government is planning to seize the powers with a bill brought to Parliament this autumn, according to the Financial Times.

Scotland's Constitution Secretary Mike Russell has previously said plans to enshrine a UK "internal market" after Brexit would seriously undermine devolution.

First Minister Nicola Sturgeon has tweeted a link to the FT report suggesting Johnson is "setting up a clash with Scotland and Wales over control of state aid" and warned the Prime Minister that he would only increase support for a Yes vote.

She wrote: "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."

The Scottish Government has already threatened to defy the legislation being considered by the UK Government, which would also see Westminster take control of food and environmental standards once powers are returned from the EU.

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SNP Westminster leader Ian Blackford also issued a rallying call to Scots. He tweeted: “This is an attack on devolution that Scotland voted for in 1997, when we overwhelmingly backed a Scots Parliament. Whilst we should be dealing with the Covid-19 crisis, we are faced with a Tory Govt engaging in a power grab against Scotland.

“Everyone in Scotland should be concerned at what the UK Govt is doing, put bluntly it is undermining our Parliament which was established by popular sovereignty. The response is simple to protect our parliament, to protect us from this type of attack we have to become independent.

“We will take this on. I call on those who live in Scotland to recognise our right to choose our future. The election result in 2019 and ongoing support in the polls indicate where the mood of Scotland is. Stay united, we will win our right to choose and secure our future.”

The UK Government told the FT that it considers state aid to be a “reserved matter”, adding that it would consult devolved governments to “seek to agree a modern system for supporting British business in a way that benefits all within the UK”.

However, European law expert George Peretz QC told the newspaper that the UK Government’s move to seize control of state aid in legislation suggested ministers are not confident of winning the argument in court.

He said the Tory government’s case is “not really arguable”, adding: “And in seeking to settle the matter through primary legislation — if that is what occurs — it looks as if the government has now agreed that it isn’t arguable either.”