Boris Johnson is in deep trouble -- even his own party is turning on him

London (CNN)Boris Johnson suffered the worst crisis of his premiership on Tuesday night, as weeks of scandal and sleaze culminated in a mass rebellion by many of his own Conservative lawmakers.

While the government ultimately won a series of votes on new coronavirus measures, it did so through the indignity of relying on opposition votes. A total of 99 Conservative Members of Parliament defied Johnson, obliterating his 79-seat majority and leaving Johnson exposed.

The question on lips in Westminster is now: How bad is this for Johnson?

In a word, very. The past two weeks have been dominated by reports that he and his team held social gatherings in Downing Street in winter 2020 while the rest of the country was under coronavirus restrictions and such gatherings were illegal.

Johnson has insisted that he believes no rules were broken, and has asked one of his top civil servants to investigate the alleged parties.

And on Wednesday an image emerged of a Christmas party held at the Conservative Party headquarters on December 14 last year.

The photo, obtained and published by The Mirror newspaper, shows 24 people at an event for Conservative London mayoral candidate Shaun Bailey at the party HQ in London.

The Tories have not responded to CNN's calls for comment on the newly uncovered photograph, but the Conservative Party had previously moved to distance itself from the event and Bailey.

The issue of Christmas gatherings, or PartyGate, as it's known, came hot on the heels of a sleaze scandal in which Johnson whipped his MPs to overturn the 30-day suspension of a Conservative colleague who had been found to be in breach of lobbying rules. Owen Patterson had sent multiple emails to government officials on behalf of two companies that between them paid him a salary of £100,000 ($133,000) as a consultant. He initially denied any wrongdoing, but eventually resigned as an MP.

There have been other scandals concerning how the PM paid for the refurbishment of his flat and who paid for a luxury holiday he took.

The pile-up of scandals and inter-party woes is a gift for Johnson's critics -- and the reports are beginning to cut through with the public, opinion polls suggest. Every week, the leader of the opposition is able to question the prime minister in parliament, and on Wednesday, Labour leader Keir Starmer twisted the knife, asking Johnson about the previous night's rebellion.

"If further votes are needed to save lives," the Labour Party would follow Starmer's leadership and help pass the essential measures if his own MPs fail to support him. Starmer asked: "Does the Prime Minister understand why his own MPs don't trust him?" Johnson declined to answer this specific question.

Starmer asked why people should follow rules that seem to be ignored by many in Downing Street. Johnson was visibly irked by this line of inquiry.

All of this has badly hurt Johnson's reputation, if personal approval ratings or polls are anything to go by. Politico's poll of polls has the Conservatives four points behind the opposition Labour Party, while 65% of people disapprove of his leadership.