On Tuesday night, the atmosphere among Conservative MPs hardened against Boris Johnson, with open discussion of how to depose him and who should follow him as he gave a catastrophic interview claiming not to have lied about Downing Street parties.

After the publishing of the Sue Gray investigation investigating accusations of lockdown breaches, a number of Tory MPs from all ranks and factions of the party stated they felt there would be enough letters to spark a leadership race, with some stories on Tuesday night suggesting it may happen sooner.

After it was revealed that a group of a dozen or so of the 2019 intake gathered in the office of Alicia Kearns to debate Johnson’s future as prime minister, Johnson was seeking to shore up his support in the parliamentary party.

After the meeting, which was termed the “pork pie putsch” since Melton Mowbray is in Kearns’ area, one MP stated there were roughly 20 letters, “some mailed, some in draft.” To trigger a confidence vote against the prime minister, 54 letters must be presented. On Tuesday evening, the prime minister met with members of the new cohort.

With MPs plotting his downfall, Johnson emerged from No 10 isolation to defend himself against charges by Dominic Cummings, his former adviser, that he lied to parliament about believing a garden party during the first lockdown was a business function.

The prime minister stated “no one warned” him that the “bring your own wine” party he attended with 30-40 employees on May 20, 2020, was against the regulations, and that he had told Gray about it.

“I can’t believe we would have gone forward with an event that was deemed illegal… Nobody informed me that was against the rules, and I am quite certain I would have remembered,” he told Sky News.

However, according to Cummings, two officials advised the prime minister against throwing a party. The Gray investigation, which is due to report next week, is slated to interview the former assistant as well.

Johnson declined to rule out resignation numerous times during his interview, and some Tory MPs fear he might opt to leave rather than face a confidence vote in the House of Commons.

Conservative MPs said they were becoming increasingly certain that Johnson will face a confidence vote, most likely when the Gray report is out.

“The tone has changed tremendously,” a frontbencher stated. He’s in a lot of trouble. It isn’t just the 2019ers that are concerned about their seats. It’s the older colleagues that are quieter. We’ll be up against it unless the report says something incredible.”

“It’s terminal,” warned another Tory MP. It has shifted from a fiery rage to a cool, calculated notion of ‘How do we do this?’ ‘And who are we backing?’ It’s a matter of when rather than if.

“Letters are coming from the left and the right, from Brexiteers and remainers, because it’s gradually dawning on people that this isn’t a policy problem; it’s an attitude, a way of doing things, and a culture that has to change.”

On Tuesday, Christian Wakeford, a 2019-intake MP, became the seventh Tory to announce that he had submitted a letter of no confidence in the government.

While Tory MPs claimed that more letters were being written and preserved as draft emails, several rebels warned their colleagues not to send them to the 1922 Committee before Gray’s report because Johnson may win a vote conducted too soon.

Johnson “will not win a vote of no confidence because there is no motivation to support him,” according to one Tory MP. “Theresa [May] had some who were afraid of what may happen next with her. “It’s a nightmare if it’s triggered before the report comes out, since it’ll be held immediately, and people won’t want to be judged before the evidence is finalized,” they added.

Tories claim there was a lot of chatter in parliament about possible leadership bids, notably by the chancellor, Rishi Sunak, who is seen to have the best operation, and Liz Truss, the foreign secretary, who is now in Australia.

Sajid Javid, Nadhim Zahawi, and Penny Mordaunt have all been mentioned as probable candidates, as have Mark Harper, Steve Baker, and Esther McVey from the lockdown-skeptic right.

Former health minister Jeremy Hunt, who ran against Johnson for the leadership, told PoliticsHome that his “ambition hasn’t fully evaporated” but that “it would take a lot to persuade me to throw my hat into the ring.”

Sunak backed the prime minister with reservations, saying he trusted his version of events. Sunak, however, when asked if the prime minister should resign if he lied before parliament, stated, “I am not going to delve into hypotheticals, the ministerial code is clear on these topics.” He then abruptly exited the interview when asked if Johnson had his unambiguous support.

Part of the pushback against Johnson has been fueled by public outrage that Tory MPs heard in their districts over the weekend. Because they are so demotivated, activists are refusing to deliver pamphlets for the next municipal elections, according to one source. Many MPs also suggested in letters to constituents that the prime minister might not be able to stay in office.

“The prime minister and the party are gravely injured in the eyes of the voters,” observed Sir Charles Walker, a former vice-chair of the 1922 Committee, in a letter to a constituent. It remains to be seen if this situation can be salvaged.”

Johnson will try to redirect the national narrative by announcing the end of Plan B Covid measures on Wednesday, when he will face tough prime minister’s questions.

Keir Starmer, on the other hand, is anticipated to stick to Johnson’s position in No 10 during lockdown. Johnson’s assertion that he was uninformed of the parties in No 10 was debunked by Starmer in an interview with the Guardian’s G2.

“This is Johnson’s third defense. After we confronted him about it in early December, he said, “I’ve been assured there were no parties,” and when the video came out, he said, “I’m outraged there have been these parties; I’ve just just found out.” And if the third defense is correct, then the previous two must be incorrect – which is a significant issue for him.”

MPs said they still don’t believe Johnson is fully aware of the peril he is in. According to one source, Johnson’s pals, notably Conor Burns and James Duddridge, asked him over the weekend if they could help him with a whipping operation to attempt to shore up support among MPs. “Until that time, he didn’t take it seriously,” one MP stated. “On his side, there has been no charm offensive. The whips have had no effect.”