British Prime Minister Boris Johnson flew home shortly after addressing the United Nations General Assembly in New York on Tuesday evening to calls for his resignation after the Supreme Court, in a landmark ruling, determined that his suspension of parliament had been unlawful. 

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PM's suspension of parliament overruled

Brexit: The knowns and unknowns

The House of Commons will sit from Wednesday morning, after 11 justices unanimously ruled that the government's move to suspend parliament for five weeks from the beginning of September was "unlawful" and "void."

The ruling was unprecedented and a severe blow to Johnson and the government. What could the short-term consequences be?

Resignation, prorogation?

Johnson, who is expected to address Parliament when it reconvenes, said on Tuesday that while the government will "respect" the Supreme Court ruling, he "strongly disagreed" with it and suggested it was part of an attempt to "frustrate" Brexit.

Labour leader Jeremy Corbyn, Liberal Democrat leader Jo Swinson and Scottish First Minister Nicola Sturgeon all called for Johnson to resign following the ruling, a suggestion dismissed by Downing Street, and opposition MPs will likely amplify that demand on Wednesday.

Members of Johnson's Conservative Party were also critical. Former prime minister John Major called for Johnson to make an "unreserved apology" but most Conservative critics trained their fire on chief adviser Dominic Cummings, who is believed to have devised the prorogation plan.

Johnson's comments suggest he will remain defiant, however, and maintain the "people versus establishment" narrative he has attempted to foster in the run up to an imminent election.

The Times newspaper reported on Wednesday that Jacob Rees-Mogg, the leader of the Commons, accused the judges of a "constitutional coup" during a Cabinet conference call on Tuesday evening.

Johnson suggested on Tuesday that he is mulling proroguing Parliament again, telling reporters "we will need a Queen's speech to set out what we are going to do." If he were to do so, the Supreme Court ruling suggests any suspension of longer than five to six days would be challenged. 

The prime minister's Conservative Party is due to begin its four-day annual conference on Sunday, and the party chairman has tweeted "of course" it will go ahead. That may mean either another prorogation or an attempt at pushing through a short parliamentary recess is imminent.

What could happen in Parliament?

The resumption of Parliament is likely to see a flurry of activity from both the government and opposition MPs, though the traditional prime minister's questions session will not take place on Wednesday.

Critics of the five-week prorogation argued that it was designed to thwart parliamentary scrutiny of the government's Brexit plans, and an immediate emergency debate on Brexit is likely. A series of further debates and committee inquiries are expected to follow.

Opposition MPs are also likely to increase pressure on Johnson to publish the legal advice for the prorogation. According to Amber Rudd, who resigned from the Cabinet this month, even senior ministers were not given sight of the case drawn up by Attorney-General Geoffrey Cox.

Will there be an election?

An attempt at forcing an election vote through either the Fixed Term Parliament Act – Johnson has already been defeated twice via this mechanism – a short law or a no-confidence vote in the government is possible.

The historic nature of the Supreme Court ruling increases pressure on the opposition to agree to an election, but Labour leader Jeremy Corbyn has reiterated that he will not back a poll until a no-deal Brexit on October 31 is absolutely ruled out.

For the opposition parties, broadly united against no-deal, a no-confidence vote risks an election before the key Brexit deadline of October 31. The Liberal Democrats have again called for a short-term unity government led by a senior MP, but Corbyn insists he must lead any alternative government.