A “major showdown” at the UK’s Supreme Court has been predicted after Scotland’s highest civil court ruled Boris Johnson’s suspension of Parliament is unlawful.

It comes after three judges at the Court of Session in Edinburgh on Wednesday found in favour of a cross-party group of politicians who are challenging the Prime Minister’s move.

Last week, Judge Lord Doherty had dismissed a challenge against the suspension of Parliament, saying it was for politicians and not the courts to decide.

The UK Government plans to appeal against the ruling and Nick McKerrell, a lecturer in law at Glasgow Caledonian University (GCU) now expects a showdown at the Supreme Court.

“This was a pretty unexpected judgment from the Inner House of the Court of Session and strongly overrules the findings of Lord Doherty’s ruling last week,” he said.

“The Lord President – the top judge in Scotland – said the decision to suspend Parliament could only be reviewed if its purpose was to ‘stymie parliamentary scrutiny’. He believed this was the true reason.

“This was because of the length of time and the documents released showing the political discussions around prorogation that took place.

“The other two judges supported this.  Significantly, all argued that in most normal circumstances the decision to prorogue could not be reviewed by the Courts which shows how exceptional this situation is.

“Ultimately then the court said the decision to suspend Parliament is ‘null and is of no effect’.

“However, this will now be appealed to the Supreme Court of the United Kingdom in London next Tuesday. This will now be a major showdown.”

Former Tory Attorney General Dominic Grieve said Boris Johnson’s position would be “untenable” and he should resign “very swiftly” if it turns out the Queen had been misled over the reasons for proroguing Parliament.

Speaking to BBC News, he said: “If it were to be the case that the Government had misled the Queen about the reasons for suspending Parliament and the motives for it, that would be a very serious matter indeed.

“Indeed in my view, it would then be the moment for Mr Johnson to resign – and very swiftly.”

He added: “I think that if that were to be the case that this had happened, Boris Johnson would find himself in an untenable position in Parliament.

“And I hope it would be untenable not just because of the opposition, but because actually every member of the Conservative Party that believes in our constitution would simply say it’s over.”

Justice Secretary Robert Buckland, commenting after reports a Downing Street source had suggested the Scottish judges were “politically biased”, said: “Our judges are renowned around the world for their excellence and impartiality and I have total confidence in their independence in every case.”

SNP leader Nicola Sturgeon said: “Today’s Court of Session judgment is of huge constitutional significance – but the immediate political implications are clear.

“Court says prorogation was unlawful and null and void – so Parliament must be recalled immediately to allow the essential work of scrutiny to continue.”

First Minister’s Questions
Patrick Harvie said criticism of the PM’s move had been ‘vindicated’ (Jane Barlow/PA)

Scottish Greens Parliamentary co-leader Patrick Harvie said: “We’ll all need to study the detail of this ruling but it seems clear that the criticism of Boris Johnson’s decision to shut down Parliament has been vindicated, and we therefore support the demand to recall Parliament.

“It’s extraordinary that the UK Government – even one which has descended ever further into minority status – should have the power to replace the Prime Minister, set the parliamentary agenda and even force MPs to pack up and go home to avoid being held to account.

“No Scottish Government would have the legal ability to act in this dictatorial manner.

“The present crisis has highlighted the urgent need for a modern, democratic constitution which prevents the abuse of power by dangerous extremists like Boris Johnson.”