However, some MPs from the 2019 intake expressed scepticism. One told The Telegraph: “I think there’s a lot of b—— being put out there about 2019 MPs. I think a lot of colleagues are holding firm rather than going wobbly.

“I don’t buy this idea that 20 letters have gone in. If the 2019 intake could organise that without briefing against each other and stabbing each other in the back, it would be a miracle.”

The plotting has infuriated senior ministers loyal to Mr Johnson, with one Cabinet source remarking: “They have fallen into the trap of thinking that the reason they were elected was because of their local campaign on potholes, rather than the PM’s appeal.”

Gary Sambrook, the Birmingham Northfield MP who is on the Government’s “watch list” of potential 2019 rebels, on Monday wrote to a constituent saying he would await the findings of Ms Gray’s report before making “final conclusions”.

But he added that “anyone who is found to have broken the law to seriously consider their position in Government, and that includes the Prime Minister”.

Among longer-serving MPs, Steve Brine, a former health minister, told a local resident that the events in Downing Street were “indefensible” and an “insult to my constituents who sacrificed so much”.

Stephen Crabb, a former Welsh secretary, said Mr Johnson “was right to apologise earlier this week, but this not be a sufficient response given the seriousness of these matters”.

It came as a new poll suggested the revelations over “partygate” had led half of voters who backed the Conservatives at the last election to form a more negative opinion of them. This rose to six in 10 when people were asked whether their views of Mr Johnson had worsened.

The growing instability surrounding Mr Johnson’s administration has encouraged a number of prominent party figures to set out their visions for getting the Government back on track.

Writing for The Telegraph, Matt Hancock, the former health secretary, called for action to curb the cost of living crisis facing families. He also raised concerns about soaring inflation sparking interest rate rises, warning: “This is by far the biggest challenge, and raises some profound questions that are simply not being debated in Westminster.”