THE political battle over Britain’s withdrawal from the EU will now be between Theresa May’s “red, white and blue Brexit versus the Tartan Remain,” Pete Wishart, the SNP’s Shadow Commons Leader, has insisted as he branded the Supreme Court case “a circus”.

His remarks came as it was announced that the Prime Minister will face senior MPs on the Commons Liaison Committee for a 90-minute hearing, which will include Brexit. It will take place on December 20, the final day of the Commons session before it rises for the Christmas recess.

Speaking during Business of the House Questions, the Perth MP launched an attack on the remarks to the court by Lord Keen, the Advocate General for Scotland, who argued that the UK Parliament was sovereign and the Sewel Convention – which states that Westminster will not normally legislate on devolved matters without the consent of Holyrood – was just that, a “political convention”.

Declaring that this week had seen “another instalment of Brexit cluelessness and chaos,” Mr Wishart referred to the Commons vote, which overwhelmingly backed the Prime Minister’s bid to get Article 50 triggered by the end of March, told MPs: “After the caving in of the Labour Party, which followed the Government’s Article 50 agenda, it’s going to be the red, white and blue Brexit versus the Tartan Remain.”

He asked David Lidington, the Commons Speaker: “Why does he not just bring forward a proper vote and end the circus in the Supreme Court. What is stopping him doing that now?”

The SNP MP said there had been “some remarkable things” said in the Supreme Court, most notably by Lord Keen, who is part of the UK Government’s legal team, who, Mr Wishart explained, “told us the Sewel Convention was merely a political act and this House can simply override the views of Scotland”.

The Nationalist spokesman said he spoke at length during the debate on the 1998 Scotland Bill when MPs were told the Sewel Convention “would be in statute, which this House passed, and we also passed the permanence of the Scottish Parliament”.

Mr Wishart added that Lord Keen’s arguments showed “massive disrespect to the views of Scotland”.

In response, Mr Lidington pointed out that almost 40 per cent of the Scottish electorate had voted to leave the EU.

He told Mr Wishart: “I can assure him that the Government is going to be, yes, looking for a Brexit that is red, white and blue but that pattern includes the flag of St Andrew and the Saltire’s interests will be very much in our minds throughout those negotiations.”

As an example of that, he pointed to the Joint Ministerial Committee, which met on Wednesday, and which brings together the UK Government and the devolved administrations to discuss Brexit.

Earlier, leading Brexiter Iain Duncan Smith issued a warning to the Supreme Court judges about upholding the earlier High Court ruling that said MPs must have a vote on Mrs May’s Brexit strategy.

He said: “I have no idea what the Supreme Court want to do but if they want a massive constitutional clash, then straying into the territory of telling parliament and government how they want to go about their business is exactly where they don't want to be."

After MPs voted to abide by the PM’s Brexit timetable, there was some anguish on Labour benches with one MP saying: “We have blundered into a Tory trap."

While there was praise on the Labour benches for Sir Keir Starmer, the Shadow Brexit Secretary, having forced the PM to come up with a plan before Article 50 is triggered, there was also a realisation that whatever she produced might not be very detailed.

However, were the judges to uphold the High Court ruling, then pressure would be back on Mrs May to produce a parliamentary Bill with some level of detail.

Those 40 or so Tory MPs who were considering rebelling before the PM produced her amendment to this week’s Labour motion but who backed off in response to it, might be minded to rebel if any Bill, as has been suggested, contains nothing more than three lines of general outline.

In court, James Woolfe, the Lord Advocate, finished his submission, arguing Westminster could change the laws of Scotland regarding Brexit but not by using royal prerogative powers.

The Scottish Government’s senior law officer argued that an Act of Parliament was required to trigger Article 50 of the Lisbon Treaty to start the two-year Brexit process and Holyrood was entitled to a voice on the issue because it involved the serious loss of EU rights for Scottish people.

Mr Woolfe said this was "a matter of significance and not simply a footnote" and it would be unlawful for the Article 50 process to start without a legislative consent motion from Holyrood under devolved legislation.

"The powers to change the laws of Scotland were given to Parliament and, of course, those Parliament has authorised and not to the Crown.

"That sets the bounds to the use of the prerogative and precludes the UK Government from asserting a power to make significant changes to laws of the land by virtue of the prerogative," he argued.

The Lord Advocate was speaking on the fourth and final day of the landmark legal battle before 11 justices over Brexit.

James Eadie QC for the UK Government is due to make his final submission later and all eyes will be on whether or not he refers to the Commons vote.

The proceedings began on Monday amid a blaze of publicity around the world. The judges are due to give their ruling in early January.