TORY ministers will use a "power grab" to "trample over Scotland" and strike trade deals with Donald Trump, a former First Minister has said.

Henry McLeish said the Tories want to hoard powers in London to prevent MSPs obstructing post-Brexit trade agreements with the US. Meanwhile, the SNP's Stephen Gethins warned that the so-called power grab would prevent Scotland standing in the way of future UK policies like NHS privatisation, or food imports of chlorinated chicken, which could form the basis of US trade deals.

After the transfer of powers from Brussels to Whitehall and Westminster, London is planning to take charge of policy areas traditionally devolved to Holyrood, but the Scottish Parliament is expected to formally reject Westminster's Brexit powers offer in a crunch vote on Tuesday.

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McLeish believes the UK wants to avoid a deadlock similar to when a free trade agreement between Canada and the EU was stalled when Belgium announced it could not sign the treaty because of opposition from regional parliaments.

"That's part of the reason for this," he said. "If the current Scottish situation evolves and more powers come to Scotland, that may make it more difficult for the UK to secure trade deals that trample over Scotland."

The Comprehensive Economic and Trade Agreement (Ceta) between Canada and the EU was on the brink of collapse after the Walloon parliament voted against it .

The Belgian region of Wallonia had been nervous about exposing its agricultural sector to competition from Canadian farmers. However, its leaders eventually dropped their opposition in autumn 2016 after concessions were made over legal safeguards.

The UK wants to retain control of 24 devolved areas, most related to agriculture, fisheries and the environment, for up to seven years, which would mean any trade deals could be signed with minimal disruption from Holyrood during that period, according to McLeish.

He warned that the Tories wanted free reign to make trade deals with "economic hard men" such as Trump, Philippines president Rodrigo Duterte, and Turkish president Recep Tayyip Erdogan.

He added: "You have to question the sincerity and the honesty of the Westminster Government. There has to be a lot of concern that the government wants to make it easy to negotiate a trade deal with those economic hard men of the Philippines, Turkey and the USA.

"If we don't contest the power grab, it will make Scotland's position much more insecure. Food standards could be undermined due to the prospect of the UK Government piggy backing on the US."

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SNP foreign affairs spokesman Stephen Gethins said people were "right to be concerned" about the impact such an arrangement could have on food imports.

He said: "People are right to be concerned that powers over fishing, farming and food standards, fracking and the environment, and other important areas are all under threat from these Tory plans to rip up the devolution settlement.

"If the price of a US trade deal was to cut our environmental standards, accept chlorinated chicken imports, or even open our NHS up to privatisation, the UK Government could end up making that deal regardless of the views of the Scottish Parliament.

"That would be completely unacceptable, so we must come to an agreement that respects devolution and the will of the Scottish people."

SNP, Labour, Green and Lib Dem MSPs are poised to vote against Westminster's EU withdrawal bill, with only the Tories expected to back the legislation in Tuesday's vote.

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Holyrood's withholding of consent for the bill means the UK Government must continue its challenge to Holyrood’s alternative Brexit Bill at the Supreme Court. The Supreme Court has provisionally set down July 24 and 25 for the legal clash.

Westminster would then be expected to take the unprecedented step of imposing its Brexit legislation on Scotland against Holyrood’s will. In response, a UK Government spokesman said: "It is the expectation of the Government that the outcome of leaving the EU will be a significant increase in the decision making power of each devolved administration."