THE battle over Brexit “probably will end up in the Supreme Court” to decide a constitutional wrangle, Nicola Sturgeon has suggested, as she stressed the Scottish Government would enter talks on Whitehall’s proposals for life outside the EU in good faith.

The First Minister also stressed Theresa May did not have a mandate for a hard Brexit ie leaving the European single market. Indeed, she pointed to the 2015 Conservative Party manifesto, which declared: “Yes to the single market.”

In an interview, Ms Sturgeon told The Herald: “The Tory manifesto could not have been clearer – ‘Yes to the single market’ - yet now they seem ready to ditch that promise to appease their hard-line Brexiteers.

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"This further underlines that there is no mandate whatsoever for a hard Brexit. The Prime Minister and her colleagues must now make clear that they will stand by their manifesto pledge, end the uncertainty and commit to maintaining the UK's absolutely vital membership of the single market," declared the FM.

Following a speech to the Institute of Directors’ annual convention in London, in which Ms Sturgeon argued that the Brexit vote was in part due to people’s disillusionment with austerity and globalisation, she raised the prospect of a political battle becoming a constitutional one in the courts.

Thus far, the Prime Minister has set her face against allowing MPs, or indeed MSPs, a vote on the UK’s Brexit proposal, claiming that the mandate for quitting the EU was given by the public in the June 23 referendum vote; having any kind of parliamentary vote could lead to a denial of that democratic mandate.

But next month, it is expected the High Court in London will hear the first of two cases, calling for MPs to be allowed to vote on the deal the UK Government proposes. It is further expected that whichever side loses, the matter will be appealed straight to the UK Supreme Court, which has the final say on matters of great constitutional importance.

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Last week, Ms Sturgeon said her administration was “keeping a very close eye” on the court actions and would assess as they proceeded whether or not Edinburgh would become directly involved.

The FM stressed she had deliberately not spoken of vetoes because “it gets you into an adversarial position at the start of a process” but she was adamant that not only Holyrood but also Westminster, Cardiff and Stormont should have votes on the Brexit proposals.

She then said: “The question of whether the House of Commons or the Scottish Parliament will have a vote will have a long way to run and probably will end up in the Supreme Court rather than just the political arena; so we will see how that goes.”

Alex Salmond, her predecessor, has made his position clear, saying: "If Scotland could block Brexit, Nicola Sturgeon should do that."

The FM stressed how the voice of Scotland, which voted 62 per cent to 38 per cent to remain in the EU, had to be heard and listened to.

She said: “I'm taking the Prime Minister at face value. We will go into this process in good faith; if we believe we are going to be involved in a meaningful way and that is the basis on which we will proceed.” The first intergovernmental talks are expected to take place before the end of October with Mrs May in the chair.

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Ms Sturgeon added: “I would argue the onus in terms of demonstrating good faith is on those who told Scotland a couple of years ago to do a certain thing in order to protect our European membership and have now brought us to the brink of EU exit.”

Meantime, Liam Fox, the international trade secretary, was accused of being vague and confused about the country's post-Brexit trading status after saying Britain would leave "no legal vacuum" with the world after leaving the EU.

The Scot told the World Trade Organisation in Switzerland that the UK would continue to uphold its international trading commitments after Brexit.

But critics said he was sending out mixed messages following weekend reports that he would use his Geneva speech to signal support for pulling the UK out of the EU customs union so he could legally strike new trade deals around the world.

Pat McFadden, Labour’s former business minister, said Dr Fox had a duty to set out the details on whether the UK would pull out of the customs union or remain a member of the single market and warned against "sleepwalking" into a trading system that relied on WTO rules because key sectors such as the car industry would face "high and destructive" tariffs.