The United Kingdom’s Supreme Court ruled unanimously on Tuesday that UK Prime Minister Boris Johnson’s decision to shut down parliament in the run-up to Brexit was unlawful.

“The decision to advise Her Majesty to prorogue parliament was unlawful because it had the effect of frustrating or preventing the ability of parliament to carry out its constitutional functions without reasonable justification,” said Supreme Court President Brenda Hale, reading out the historic decision.

“Parliament has not been prorogued. This is the unanimous judgment of all 11 justices,” she added.

“It is for parliament, and in particular the speaker and the (House of) Lords speaker, to decide what to do next.”

Scotland’s First Minister Nicola Sturgeon said Johnson was unfit for office and if he did not resign he should be forced out. 

Speaker John Bercow said the House of Commons must convene without delay. 

“As the embodiment of our Parliamentary democracy, the House of Commons must convene without delay,” Bercow said.

“To this end, I will now consult the party leaders as a matter of urgency.”

Opposition leaders demanded Johnson resign, saying he has misled the queen. 

Sturgeon said: “This is the most significant and historical constitutional court ruling that we’ve had in all of our lifetimes. 

“Boris Johnson should resign, this is a prime minister who has been found by the UK Supreme Court to have acted unlawfully, seeking to evade scrutiny without good reason. 

“If the prime minister isn’t prepared to do the decent and honourable thing in tendering his resignation, then I think parliament should quickly come together to force this prime minister from office.”

British Labour Party leader Jeremy Corbyn told delegates at Labour’s annual conference in Brighton: “I invite Boris Johnson, in the historic words, to ‘consider his position.”

UK Liberal Democrat leader Jo Swinson said Johnson was unfit to rule and that she was returning to Westminster to take up the fight against Brexit. 

“He’s misled queen and country, and unlawfully silenced the people’s representatives.

“I’m on my way to resume my duties in the Commons and stop Brexit altogether,” Swinson said.

The Supreme Court said the UK government had provided no reasoning for the decision to suspend parliament. 

“It is impossible for us to conclude, on the evidence which has been put before us, that there was any reason – let alone a good reason – to advise Her Majesty to prorogue Parliament for five weeks,” the judges said in their ruling.