Boris Johnson’s landslide general election victory in 2019 secured his position in Number 10, but he can only stay in post with the backing of Conservative backbench MPs.
A leadership vote is looking more likely as MPs react to the findings of the Sue Gray report into lockdown-breaking parties in Number 10 and Whitehall, released in late May, and the Met Police’s investigation that concluded in late April.
Dozens of Conservative MPs have publicly called for Mr Johnson to go, increasing speculation the 54 letters needed to trigger a leadership vote could be reached soon.
What would it take for the PM to be ousted by his party, and how would the process work?
Letters of no confidence
Conservative MPs can send letters of no confidence in the PM to the influential 1922 Committee of Tory backbench MPs at any time.
The committee meets weekly when parliament is sitting, with the gatherings usually providing an indicator of backbench support for the leadership, direction of the party or major policies.
Often referred to as “the men in grey suits”, the 1922 Committee is led by an 18-member executive committee with a chair elected by committee members.
MPs disgruntled with their party’s current leadership can submit no confidence letters to the committee’s chairman, registering their disapproval.
The Conservative Party rules state that at least 15% of Tory MPs must write a no confidence letter to make a leadership challenge possible.
This figure currently equates to 54 Conservative MPs needing to submit a letter to 1922 Committee chairman Sir Graham Brady.
Letters are handed in confidentially, so no accurate total of how many have been submitted to Sir Graham is publicly available. He is therefore likely the only person who knows the real tally.
In 2018, when former prime minister Theresa May faced a no confidence vote after the then threshold of 48 letters was reached, Sir Graham said not even his wife knew how many MPs had written to him.
At the time, only 24 MPs had publicly revealed they had handed in letters.
Image: Theresa May survived a bid to oust her in 2018
A vote on the party leadership
If Sir Graham receives 54 letters from backbench Conservative MPs, a vote of no confidence in Mr Johnson would be triggered.
It will take place in the form of a secret ballot where all Conservative MPs will have to decide if they back the current leader or not.
The ballot is usually open for a few hours on one particular day, and Mr Johnson would have to secure the backing of half of his MPs plus one to survive.
If a vote did take place and Mr Johnson was to gain the backing of the 180 MPs needed he would be immune from a further challenge for another year.
If he were to lose, there would be a leadership contest and he would be barred from entering.
However, if Mr Johnson were to just scrape enough votes to allow him to stay on, he could decide to stand down of his own accord – automatically triggering a leadership contest.
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A leadership contest
If a Conservative Party leader does not secure the confidence votes required, a leadership contest will be held to replace them.
The 1922 Committee would set the timetable for the contest.
To take part in the race, a Tory MP has to be nominated by eight colleagues.
If more than two MPs put themselves forward and secure enough nominations to run for leader, a series of secret ballots will be held to whittle them down.
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The individual who receives the fewest number of votes will be eliminated after every round until two candidates remain.
When just two MPs are left in the race, party members get to make their final choice before a deadline set by the 1922 Committee.
The winner will become Conservative Party leader and PM if the party is in power and a general election is not held.
