But what exactly is a no-confidence motion and how does it work?
Technically any MP can bring forward a motion of no-confidence, which includes the leaders of the SNP and the Liberal Democrats. The SNP have flagged lodging the motion as early as today or tomorrow.
However, to be guaranteed a debate and vote, the move has to be brought by the leader of the official opposition, which in this case is Labour leader Jeremy Corbyn.
Why the goal posts have shifted
Mr Johnson, who has publicly said he is happy to go to a general election, shifted the goal posts on this convention last week by telling MPs in the Commons he would allow time for a confidence motion tabled by any of Westminster’s parties.
He said MPs should have the “courage” to table a motion, adding: “This parliament must either stand aside and let this government get Brexit done, or bring a vote of confidence and finally face a day of reckoning with the voters.”
A clear majority is all that is required for the motion of no confidence to be successful.
Mr Johnson has maintained a 100 per cent losing record as PM after MPs last week refused to allow him to shut Parliament down for this week's Conservative Party conference.
What happens if the Government loses the vote?
If the government loses a motion of no confidence, the Fixed Term Parliament Act (FTPA) outlines a 14-day period in which an administration can be formed.
The prospective government, which in this case could be led by a temporary prime minister such as Mr Corbyn, must be able to pass a confidence motion in this period.
The SNP’s theory is that a caretaker prime minister will be installed in this period and would head off to Brussels to request an Article 50 extension, guaranteeing the UK did not crash out of the EU without a deal on 31 October, before calling a general election.
However, if Westminster’s political parties failed to coalesce around one figure who can command a majority in the House of Commons during this 14-day period, a general election will automatically be triggered.
The second option open to MPs
Lord Norton of Louth, one of the world's leading authorities on Parliament, has explained a secondary option.
He told LBC radio: "What's being talked about at the moment is possibly moving a motion that expresses no confidence in the Government, but not in the form of words stipulated by the FTPA.
He added: "So the Commons could demonstrate it has withdrawn its confidence from the Government, but that would not trigger an early election because it's doesn't engage any provisions of the FTPA."
Lord Norton outlined that if the House expresses no confidence in the Government in whatever form, the Government cannot continue, but it does not stipulate who would then take over.
A 'unifying' figure other than Mr Corbyn to act as interim prime minister remains a possibility. Former Labour deputy leader Dame Margaret Beckett has been among compromise options put forward.
But Lord Norton has clarified under this scenario, Mr Johnson wouldn't necessarily be legally required to resign.
Lord Norton said: "Convention would be that the Prime Minister would be expected to resign, but there's no formal requirement or statutory requirement."
He added: "That is governed by convention not by any formal rule that is enforceable."
Mr Johnson's refusal to resign would leave the Queen in a particularly difficult position.
Lord Norton outlined: "The position is that the Prime Minister remains the Prime Minister until such a time as the Prime Minister resigns. Formally, one serves at the pleasure of the sovereign. So, technically, the sovereign could dismiss a prime minister but in practice, in the era of modern British politics that doesn't happen."