Nicola Sturgeon has demanded Boris Johnson resign as Prime Minister after judges at the UK’s highest court unanimously ruled his decision to suspend Parliament was unlawful.

The 11 Supreme Court justices agreed on Tuesday that the five-week prorogation in the run-up to Brexit was “void and of no effect”.

As well as calling for Mr Johnson to step down, she demanded the UK Government make clear it will not take the UK out of the EU without a deal on October 31.

Following that, Ms Sturgeon said there should be a general election as it is “impossible to have confidence in this Prime Minister or the Government he leads”.

In a statement to MSPs at Holyrood, the First Minister said the Prime Minister’s actions in proroguing Parliament unlawfully “shames his office, it shames the UK Government, it shames the Conservative Party”.

Ms Sturgeon said: “It was Boris Johnson who took the decision to prorogue Parliament.

“It was Boris Johnson who acted unlawfully, and I do not say this lightly, but it is Boris Johnson who must now resign.”

She added: “It is of course possible for a Prime Minister to continue in office if they are unpopular.

“It is even possible for a Prime Minister to survive in office if they are not competent.

“But no Prime Minister should believe they can act with impunity and remain in office when they have acted unlawfully in the manner and in the circumstances set out so clearly by the Supreme Court today.”

A No 10 source has already said: “The PM will not resign following the judgment.”

Ms Sturgeon responded: “The view that he should resign today is not just about politics – it should be the conclusion of anyone who believes parliamentary democracy, accountability and the rule of law matter.”

Following the landmark verdict, the Scottish Tories’ acting leader Jackson Carlaw told MSPs the UK Government has to accept the decision.

Speaking after Nicola Sturgeon addressed the Scottish Parliament, Mr Carlaw said: “Today’s judgment by the Supreme Court is as profound as any made by any court in my political lifetime.

“The judgment of the courts must be respected by Government, all the more so when it may not like the result.

“The judgment clearly upholds the principle that government is subject to the will of parliament and that parliament is therefore not subject to the will of government – an important consideration for each of us in every parliament.”

Mr Carlaw, who is standing in as leader following the resignation of Ruth Davidson, urged MPs to work to get a deal with the EU, and asked Ms Sturgeon whether the SNP would vote for a hypothetical Brexit deal negotiated with European leaders.

Scottish Labour’s Alex Rowley added to the calls for Mr Johnson’s resignation, arguing his actions have shown “contempt for democracy” and describing the prorogation of Parliament as “an abuse of power by the Prime Minister”.

Ms Sturgeon replied: “I don’t think we should allow the extraordinary nature of what the Supreme Court has said, and the significance of that, to somehow be normalised in the midst of the chaos that the UK and UK politics has descended into.

“This is an unprecedented judgment, it is truly historic.

“The Prime Minister has been found to have acted unlawfully in a manner and circumstances that I think makes his continued tenure as Prime Minister unthinkable.

“I think that if he has any honour then he will tender his resignation in light of this judgment.”

Scottish Greens MSP Patrick Harvie said the UK “now has a rogue Government which cannot in any respect be expected to respect democracy and the rule of law”.

He added: “He is someone who throughout his career has shown contempt for the truth, he has shown contempt for Parliament, he has shown contempt for devolution and – even though it’s out of character for me to stand up for the Queen – he’s shown contempt for a monarchy that he professes to believe in.”

Supreme Court rules PM Boris Johnson went beyond his powers with prorogation move