THE Scottish Government has threatened to defy proposed UK legislation allowing Westminster unilaterally to set food and environmental standards, setting the stage for the biggest constitutional stand-off between London and Edinburgh since the 2016 Brexit referendum.

Michael Russell, Scottish Secretary for Constitutional Affairs, told the Financial Times that his government was prepared to fight in the courts over UK legislation that would aim to give Westminster unilateral control over standards in a bid to create a single UK market.

The bitter dispute over the Conservative Government’s efforts to ensure it has a free hand in post-Brexit trade negotiations with other countries highlights the far-reaching constitutional implications of leaving the EU.

One person familiar with the proposed UK single market bill said it would create powers to enable the Westminster Government to force Scotland and Wales to accept whatever new standards on food, environment and animal welfare were agreed in future trade agreements.

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Food safety, agriculture and many aspects of the environment are policy areas overseen by the devolved administrations in Edinburgh and Cardiff, but the UK Government wants to have the final say on issues previously decided in Brussels.

Russell said the Scottish administration accepted the need for “common frameworks” across the UK and had been working with British government officials to try to agree them in contested policy areas.

But he went on to accuse British ministers of “bad faith” in proposing a statutory framework for the UK market that would allow them to “impose what they like”. “We do not accept that this is a legitimate way of operating within devolution,” said Russell.

“[If] they pass legislation … then we will have no intention of implementing that and they would have to essentially go to court to force its implementation.”

That could pave the way for a court battle over a UK Government attempt to curb Holyrood's powers in the run-up to Holyrood elections in May 2021 that opinion polls suggest the SNP is on course to win by a large margin.

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It highlights how the planned UK single market bill could unleash further significant tensions between London and Edinburgh since the Brexit referendum, when Scotland voted to stay in the EU.

Welsh as well as Scottish ministers are concerned by proposals in the legislation for a “mutual recognition” regime that could force them to accept controversial products such as chlorinated chicken from the US.

The UK Government has pledged to defend food and environmental standards in future trade negotiations, but farming, environmental and animal welfare groups are alarmed at its refusal to enshrine those promises in law.

A so-called white paper on the UK single market bill is expected in the coming weeks, and the UK Government plans to rush through the legislation in the autumn.

Trade experts said it has long been recognised that negotiating trade deals on behalf of the entire UK could create friction between the Westminster government and the devolved administrations, which want to maintain strict EU rules on matters such as genetically modified crops and safe levels of pesticide residues.