How are they going to do that? Jeremy Corbyn has suggested he could push a vote of no confidence in Johnson during the first week of September.
If Johnson wins? Then he remains PM. However the Labour leader can call as many no confidence votes as he likes.
If Johnson loses? A 14-day countdown begins. If Johnson or another alternative government is unable to prove it has a majority in this time, a general election is triggered.
Will he lose? Johnson has a majority of just one. And two Tory MPs, Dominic Grieve and Ken Clarke, have indicated they would be prepared to take the nuclear option of voting to bring down their own government in order to stop no-deal. It will be close.
So an election in October then? An election would take place 25 working days after parliament was dissolved. Which means it would take place just days before the October 31 Brexit deadline.
Not so fast. But as the House of Commons library explains, it is up to the prime minister to recommend a suitable polling day to the Queen. And Johnson has not ruled out delaying any election until after October 31.
This would ensure it would be too late for any new PM to delay or reverse Brexit. The UK would leave the EU with no-deal during the election campaign.
Woah there. Corbyn has written to Sir Mark Sedwill, the cabinet secretary, demanding he declare this to be “unconstitutional”.
He argues election ‘purdah’ rules mean decisions on which a new government “might be expected to want to take a different view” should be postponed until after polling day.
Corbyn asked Sedwill to confirm that if the UK is due to leave the EU without a deal while an election is under way, the government should seek another time-limited extension to Article 50 to allow the voters to decide.
Can the Queen fire Johnson? It has been suggested if Johnson refuses to resign immediately as PM after losing a no confidence vote, the Queen could sack him.
Robert Hazell, professor of government and the constitution at UCL, points to the Cabinet Manual when he argues if during the 14-day period MPs have “clearly indicated support for an alternative prime minister” then it would be expected of Johnson that he resign. “If he refused to do so, the Queen would be entitled to dismiss him and appoint the alternative as prime minister,” he writes.
But would she want to? The last time the monarch got rid of a PM was in 1834. Resurrecting the power would be deeply controversial. As the manual notes in an understated manner: “In modern times the convention has been that the Sovereign should not be drawn into party politics.”
Will Jeremy Corbyn become PM? John McDonnell has said if Johnson loses a no confidence vote then he has to be replaced with a Labour government. “I would be sending Jeremy Corbyn in a cab to Buckingham Palace to say we’re taking over,” he told the Edinburgh Fringe.
Wait, can you do that? Dr Catherine Haddon from the Institute for Government (IfG) said the shadow chancellor should perhaps “cancel that Uber” before he gets overexcited. “No you can’t just show up in a cab at the gates of Buckingham Palace and get made PM,” she said. Otherwise everyone would be doing it.
Maddy Thimont Jack, also of the IfG, explained to HuffPost UK as the leader of the official Opposition it would “reasonable” for Corbyn to think he had first dibs to takeover. “Although, the Queen would also likely be guided by the politics at the time if this process was triggered,” she added.
And the politics are murky. It is not yet clear whether opposition parties including the SNP and the Lib Dems would be keen to put Corbyn in No.10.
Ok, what about a government of national unity? One other option would be for backbenchers opposed to a no-deal Brexit from various parties to club together under the leadership of a senior MP.
Led by? Yvette Cooper, Ken Clarke, Keir Starmer and Dominic Grieve have all been mentioned.
Will it happen? Unlikely. The Labour leadership has rejected the idea of taking part, making it hard to see how any unity government could get the numbers required to form a majority.
Who would win a general election? Ask again later.