Johnson has weathered many storms during his time as prime minister, but this could be a crisis.
Here’s what you need to know.
The immediate cause of the crisis was the fallout from the resignation of deputy chief whip Chris Fincher last Thursday, amid allegations that he groped two guests at a private party the night before.
What got Johnson into deep trouble were the confusions Downing Street press officers faced when trying to explain why Fincher was ever in government.
At first, when new reports about Mr Pincher’s historic behavior emerged in light of his resignation, Downing Street denied any knowledge of the allegations relating to the prime minister’s time as Foreign Office minister.
When it became clear this would not happen, Johnson’s team said it was aware of the historical allegations, but that they were “exhausted”.
When one of the previously unreported charges against Pincher appeared to have been confirmed, Johnson’s spokesman explained that “resolved” meant confirmed.
On Tuesday morning, Simon Macdonald, a former top civilian employee of the Foreign Office, revealed that Johnson had been told in person of the outcome of the investigation into Fincher’s conduct, which eventually sparked a wave of resignations.
What happens next?
Boris Johnson is still in control of his own destiny … this time.
Conservative Party rules rule that if a leader wins a confidence vote, they are immune from another challenge for 12 months. Johnson survived a confidence vote on 6 June.
However, the current crisis is so deep that in 1922 a group of Conservative backbench MPs could rewrite the rules to remove the Prime Minister.
The committee met on Wednesday and decided to hold elections for the new leadership on Monday. Once elected, the committee’s new executive will decide whether to change the rules and move forward with another confidence vote — which Johnson is likely to lose.
Until then, the question is how much public humiliation Johnson can take. Dozens of lawmakers have now quit the government and a delegation of cabinet members descended on Downing Street on Wednesday evening to call on the prime minister to resign.
One of them — UK Home Secretary Priti Patel — told Johnson the party’s general view was that he should go, a source close to Patel told CNN.
More government ministers are almost certain to quit and opposition sources are talking about the possibility of defections.
What happens if Johnson resigns?
In the UK, the resignation of a prime minister does not automatically trigger a general election.
If Johnson steps down, the Conservative Party will hold an internal election to choose a new leader, who will then become prime minister.
Like his predecessors Theresa May and David Cameron, who resigned in May 2019 and June 2016 respectively, Johnson will remain in office until his successor is chosen.
Barring another resignation or snap election, the new prime minister will lead the UK until the next scheduled election in 2024.
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