Boris Johnson will face a confidence vote in his leadership of the Conservative Party after enough MPs submitted letters calling for a contest.

It will take place between 6pm and 8pm this evening in the House of Commons and an announcement is expected about an hour after the vote closes.

After months of speculation, it has been confirmed that at least 54 MPs – 15% of Tory MPs – have written to the chair of the 1922 Committee, Sir Graham Brady, calling for a vote.

He said he notified the PM on Sunday that the threshold had been reached and they agreed on timings together.

Sir Graham said he would not reveal when the threshold had been reached but it would “not be wrong” to say some MPs had asked for their letters to be post-dated to ensure the Queen’s Platinum Jubilee celebrations were not interrupted.

For the PM to be ousted, half of Tory MPs plus one would need to vote against him, which is currently 180 MPs.

The letters came after a sustained period of pressure on the prime minister over partygate, revelations of lockdown-breaking events in Downing Street and across Whitehall during pandemic restrictions in 2020 and 2021.

Mr Johnson was fined for attending his birthday party in the Cabinet Room in Number 10 in June 2020. His wife Carrie Johnson and Chancellor Rishi Sunak were fined for the same event.

The Metropolitan Police investigation into partygate finished in May, with 126 fixed penalty notices issued to 83 people.

Despite expectations that the prime minister would receive more fines on top of the fixed penalty notice for his birthday party, he was issued with only one.

This was viewed as a boost for Mr Johnson, but the publication of senior civil servant Sue Gray’s damning full report into partygate put his position in fresh peril.

Her findings pushed enough Conservative MPs to submit letters and the prime minister now faces a vote in his leadership a little under two and a half years after he won the biggest Tory majority since the 1980s.

How the vote will work

Mr Johnson will have to secure the backing of half his MPs plus one to survive – 180 votes.

If he wins, he will remain as party leader and prime minister and be immune from another such challenge for a year.

But if he loses, a contest to choose a new party leader and prime minister will take place, with Mr Johnson barred from standing.