Another Tory MP has confirmed they have written a letter of no confidence in Boris Johnson.
John Stevenson is the 17th Conservative MP to confirm they have sent a letter to the 1922 committee.
Twenty-one others have said Mr Johnson should resign over the partygate scandal, but not confirmed they have submitted letters.
Revealing the move on Tuesday, the Carlisle MP said a confidence vote was “the only way we are to draw a line under all the recent issues surrounding the activities in Number 10.”
In a statement he added: “Sadly, the Prime Minister appears unwilling to bring matters to a head and submit himself to such a vote.
“Therefore, the only option is for the Conservative MPs to facilitate a vote of confidence. I have already take the appropriate action.”
The Prime Minister will face a confidence vote if 54 Tory MPs write to Sir Graham Brady, the chairman of the backbench 1922 committee, demanding one be held.
— John Stevenson MP (@John4Carlisle) May 31, 2022
Half of Conservative MPs would then have to vote for the Prime Minister to face a leadership contest.
Eighteen Tory MPs have confirmed that they have written to Sir Graham, while another 21 have publically called for Mr Johnson to resign but not confirmed a letter.
A further 32 Tory MPs have publicly criticised Mr Johnson over the partygate scandal.
Four London MPs, Sir Bob Neill (Bromley and Chislehurst), Stephen Hammond (Wimbledon), Elliot Colburn (Carshalton) and David Simmonds (Ruislip, Northwood and Pinner) have so far called on Mr Johnson to stand down.