Boris Johnson went odds-on on the Betfair Exchange to face a vote of no confidence in June as Conservative MPs expressed concerns about his leadership.
The prime minister hoped to put his problems behind him following the publication of the Sue Gray report into partygate last week.
But he has been heavily criticised by Tory MPs, including Angela Leadsom, and calls for a no confidence vote have gathered pace in the past 24 hours.
That's reflected in the betting where Johnson is 1.558/15 to face a no confidence vote in parliament this month.
At least 30 MPs have said the prime minister should resign or call a confidence vote but not all have confirmed they have submitted a letter to the 1922 committee.
Johnson is 4.67/2 to leave office this month and 2.3811/8 to be gone by the time of the Conservative Party conference in September.
He is 2.245/4 to leave this year - the shortest price in the market - 2.427/5 to be the Conservative leader at the next general election which is scheduled for May 2024.
Graham Brady, chair of the committee, would not say how many letters had gone calling for the PM to go.
There are believed to be 18, although Dominic Raab said this morning there was around 30. It would take 54 to trigger a confidence vote.

With the Bank Holiday weekend beginning tomorrow, to coincide with the Queen's platinum jubilee, the earliest the vote would take place would be next week.
The Conservatives face two tricky by-elections this month in seats they won at the last general election.
They take place in Wakefield, Yorkshire and in Tiverton and Honiton, Devon on 23 June.
Labour are 1.051/20 to win in Wakefield while in Tiverton and Honiton the Liberal Democrats are 1.292/7 even though they need to overturn a Conservative majority of 24,000.
Follow our politics live blog for more updates.