Boris Johnson has quit as an MP with immediate effect - and criticised Rishi Sunak in a blistering resignation letter.
The former prime minister also attacked the panel of MPs who are investigating whether he lied to the Commons over partygate.
The privileges committee has now confirmed it will meet on Monday to conclude its inquiry, with a spokesman vowing to publish its report "promptly".
In a combative 1,000 word statement, Mr Johnson claimed:
• A "tiny handful of people" are using their investigation to "drive him out" of parliament
• MPs on the privileges committee haven't "produced a shred of evidence" to suggest he misled the Commons - and their report is "riddled with inaccuracies and reeks of prejudice"
• The committee is a "kangaroo court" that is determined to find him guilty
• A "witch hunt" is under way to "take revenge for Brexit" and reverse the referendum result
• The Conservatives' gap in the polls has "massively widened" since he left power, and taxes must be cut
Mr Johnson was especially critical of Labour MP Harriet Harman, the chair of the privileges committee, and alleged that she was overseeing a panel driven by "egregious bias".
His resignation means Rishi Sunak now faces the prospect of two by-elections, with Nadine Dorries - one of Mr Johnson's closest allies - also announcing on Friday that she was vacating her seat effective immediately.
The Conservatives may face an uphill struggle to hold on to Mr Johnson's seat in Uxbridge, west London, with polling data from Savanta suggesting that Labour currently has a 14-point lead in the constituency.
'Procedure followed at all times'
The privileges committee, meanwhile, hit back at Mr Johnson's comments in a statement - insisting that proper procedures had been followed "at all times" and would continue to be so.
A spokesperson said: "Mr Johnson has departed from the processes of the House and has impugned the integrity of the House by his statement."
The cross-party privileges committee, which is led by Ms Harman but has a Tory majority, has been assessing whether Mr Johnson misled parliament with his statements claiming all COVID rules and guidance were followed by Number 10 during lockdown gatherings.
Mr Johnson was facing the prospect of a by-election if MPs recommended a suspension from the Commons of 10 days or more as a punishment for lying.
Public 'sick of never-ending Tory soap opera'
Conservative MP Sir Michael Fabricant - who received a knighthood in Mr Johnson's resignation honours list on Friday - said the former prime minister had been the subject of "disgraceful treatment".
He tweeted: "Disgraceful treatment of a political leader who has made world history by achieving Brexit and leading the Conservatives to a landslide general election victory."
Richard Mills, chairman of Uxbridge & South Ruislip Conservative Association, said it had been an "honour and privilege" to work with Mr Johnson since he was elected in 2015 - and called his commitment to the constituency over the last eight years "outstanding".
Former Tory MEP and current chair of the Conservative Democratic Organisation, David Campbell Bannerman, also said he believed Mr Johnson would return to politics in the future.
Speaking to BBC Newsnight, Mr Campbell Bannerman - who served as UKIP deputy leader from 2006 to 2010 - said: "There are big questions about the fairness of this [privileges committee] procedure.
"I think it is a very bad day for democracy, and Boris is right to call it undemocratic.
"And I do hope that he does come back - I believe he will."
When challenged on the fact that four out of seven of the MPs on the privileges committee are fellow Conservatives, he said: "I've got respect for them as individuals - I know them well - but I'm afraid the way this was conducted was outrageous."
'He blames everybody but himself'
However, many MPs have welcomed Mr Johnson's departure.
Deputy Labour leader Angela Rayner said: "As Boris Johnson exits in disgrace, the British public are sick to the back teeth of this never-ending Tory soap opera played out at their expense.
"After 13 years of Conservative chaos, enough is enough. It's time for a fresh start for Britain with a Labour government."
Green MP Caroline Lucas tweeted: "Everyone knew he was not fit to hold public office before he was even an MP. Yet Tories made him their leader and look what happened. Evading scrutiny to the last and choosing to quit just hours after gifting gongs and peerages in atrocious act of patronage and sleaze."
Meanwhile, former Number 10 communications chief Alastair Campbell said: "His statement is utterly Trumpian.
"It blames everybody but himself - it rewrites history."
Former Tory MP Anna Soubry also told Sky News that she believed Mr Johnson had resigned because he feared he would lose a vote on any punishment recommended by the privileges committee in the Commons.
"It's really important to remind everybody that this privileges committee has a Conservative majority," she said.
"The idea that this is some sort of stitch-up is for the birds."