Boris Johnson is set to face an increasingly angry chorus of his own MPs amid reports the 54 letters which would launch a no confidence vote in the PM could be received on Wednesday.

Reports on Tuesday night suggested MPs furious at the Prime Minister’s handling of the partygate scandal engulfing Westminster had been angered further by Mr Johnson’s insistence that nobody had told him a party at Downing Street would break rules he himself had set.

And that especially those in the 2019 intake, many of whom have slim majorities after votes were “lent” to them during the last election, were preparing to submit their letters to the chairman of the 1922 Committee of backbench MPs, Sir Graham Brady.

Bury South MP Christian Wakeford – who has a majority of just 402 – became the seventh Conservative MP to publicly call for Mr Johnson to go on Tuesday, according to Yahoo News.

But a number of newspapers reported that the plot to oust Mr Johnson was far wider, as the PM will attempt to reassure his party when he appears in the Commons for Prime Minister’s Questions on Wednesday.

An expected announcement that Plan B measures to stem the spread of coronavirus will be lifted next week is likely to please some backbenchers.

But MPs from the former so-called Red Wall were said to have met on Tuesday to discuss Mr Johnson’s future in a gathering nicknamed the “pork pie plot” or the “pork pie putsch”, and one told The Daily Telegraph the 15% of letters needed to trigger a challenge could be reached on Wednesday.

Mr Johnson, who was reported to have spent Tuesday evening in his Commons office meeting with potential rebels, apologised multiple times in a major broadcast interview for “misjudgments that were made”.

But he stuck to his defence that he had thought a “bring your own booze” party held in the No 10 garden on May 20, 2020 had been a work event and he had not been warned about it in advance.

Mr Johnson’s former chief aide Dominic Cummings threw that into doubt on Monday as he said he would “swear under oath” Mr Johnson was told about the bash.

But asked if he had lied to Parliament over the parties as he visited a north London hospital, the PM told broadcasters: “No. I want to begin by repeating my apologies to everybody for the misjudgments that I’ve made, that we may have made in No 10 and beyond, whether in Downing Street or throughout the pandemic.

“Nobody told me that what we were doing was against the rules, that the event in question was something that… was not a work event, and as I said in the House of Commons when I went out into that garden I thought that I was attending a work event.”

Mr Johnson said he “can’t imagine why on Earth it would have gone ahead, or why it would’ve been allowed to go ahead” if he had been told it was anything but a “work event”.

“I do humbly apologise to people for misjudgments that were made but that is the very, very best of my recollection about this event,” he said.

Mr Johnson confirmed he had given evidence to an inquiry being carried out into Whitehall parties during lockdown restrictions by senior official Sue Gray.

And the PA news agency understands Mr Cummings has also agreed to speak to the civil servant who has been described as “formidable”.

Chancellor Rishi Sunak refused to give the Prime Minister his unequivocal backing on Tuesday, as Mr Johnson made his first public appearance after reducing his contacts last week, when No 10 said a family member had tested positive for Covid-19.

But Culture Secretary Nadine Dorries came out to bat for the PM, telling The Times those manoeuvring against him were “being disloyal to the Prime Minister, the party, their constituents and the wider country”.

Mr Johnson insisted he only saw the “bring your own booze” invite his principal private secretary Martin Reynolds sent to more than 100 staff “the other day… when it emerged”.

He declined to say whether he would resign if it was proved he did intentionally mislead Parliament, instead pleading for patience ahead of Ms Gray delivering the verdict of her partygate inquiry, which is not expected until the end of this week at the earliest.

He appeared distressed as he faced questions about two events in No 10 last April on the eve of the Duke of Edinburgh’s funeral, during which the Queen sat alone as she mourned.

The Prime Minister audibly breathed heavily behind his mask as he said: “I deeply and bitterly regret that that happened.

“I can only renew my apologies both to Her Majesty and to the country for misjudgments that were made, and for which I take full responsibility.”

Of those Tory MPs withholding their judgement for now, many accepted that if Mr Johnson was found to have misled Parliament, he would have to resign.

Deputy Prime Minister Dominic Raab accepted Mr Johnson would “normally” be expected to resign if he intentionally misled Parliament, while Mid Derbyshire Conservative MP Pauline Latham told Times Radio: “If he has lied to Parliament, there will be no choice.”

She said: “At the end of the day, he made the rules, he was in that briefing room looking at the cameras saying this is what you have to do. So you can’t say didn’t know what the rules were. We all knew what the rules were.”

Deputy Labour leader Angela Rayner said Mr Johnson “needs to go”.

“I think he’s trying to take the British public for fools. He’s not sorry that he clearly attended a party, knows it’s against the rules; he’s sorry he got caught for it,” she told the PA news agency.

“I think people are incredibly frustrated.”

But she added: “He won’t, of course, and now it’s up to his MPs to do the right thing.”