Lord Geidt was seething with anger.

First, the British prime minister had broken his own lockdown rules and received a fine from the police. Then Geidt, his ethics chief, had asked him repeatedly to explain to the public whether his actions broke the ministerial code. The requests had been met with a wall of silence. 

Now, Geidt was facing up to Boris Johnson for a final time. He threatened to resign. 

For months, Johnson has clung on to power. Rumours of lockdown breaches, an investigation by the Metropolitan Police and even a damning reportSenior civil servant Sue Gray's report into allegations of parties at Downing Street during coronavirus lockdown restrictions was published last week.  into drunken party culture at Downing Street all failed to take him down.

But some think this latest blow could be deadly. The timing of Lord Geidt's resignation threat - a sudden bombshell on Tuesday morning before Parliament broke up for the Jubilee weekend - is key.  

When MPs return on Monday morning, Conservative backbenchersMembers of Parliament who are not part of the government or shadow cabinet. They sit on the backbenches of the House of Commons.  may finally have submitted enough letters to the 1922 Committee to trigger a vote of no confidence. "The fuse is getting closer to the dynamite here," remarked former ToryA member of the Conservative party.  leader William Hague. 

Johnson and his allies insist he has not broken the ministerial code - the set of rulesThe rules include an "overarching duty" to follow the law. Johnson insists that "paying a fixed penalty notice is not a criminal conviction".  that government ministers must follow. They say it is a matter of intent: yesterday, deputy prime minister Dominic Raab said Johnson had broken the law only "inadvertently". 

Moreover, Johnson's supporters argue it would simply not be in the best interests of the Conservative party to oust the prime minister. Boris Johnson is a proven election winner. He has no clear replacement.

But others bitterly disagree. And they have the lessons of history on their side. 

Since the end of World War Two, the Conservatives have made a habit of swapping prime ministers. Six different leaders, including Boris Johnson and Theresa May, entered Downing Street without winning a general election. All but one then went on to win the next election.

Yet when the Tories have clung on to ailing prime ministers, misfortune for the party has soon followed.

In 1995, John MajorMajor was the British prime minister from 1990 to 1997.  resigned as party leader but then won his role back in a leadership contest. Two years later, the party suffered a landslide defeat to a young Tony BlairTony Blair was the leader of the Labour party. He was British prime minister from 1997 to 2007. . 

Boris Johnson and John Major's troubles are very different. Major was weakened by Black WednesdayOn 16 September 1992, the collapse of the pound forced the UK government to withdraw from the European Exchange Rate Mechanism. and the collapse of the British pound. Meanwhile, Johnson is facing fury for law-breaking parties. But incredibly, at 64%, their dissatisfaction ratings from the public are exactly the same. 

"The disasters, debacles and scandals that break prime ministers are unique events," summarises journalist Peter Franklin. 

"Therefore there's no point in questioning the 'seriousness' of Partygate. The only relevant question is whether the Boris is broken or not. If he is, then history teaches his party what to do about it."

Only time will tell whether Johnson will hold on to power. But one thing is clear: his fate will determine the future of British politics for years, perhaps even decades, to come.

Yes: Boris Johnson is the ultimate political survivor. He has faced months of allegations, accusations, investigations and calls to resign. Lord Geidt's threat will not stop him now.

No: Conservative MPs are beginning to realise that Partygate will not go away. Boris Johnson is becoming a liability to his own party. He may not resign, but he will soon be forced out of office.

Or... Lord Geidt's resignation threat may not be a fatal wound for Boris Johnson, but he will not lead the Conservatives into the next election. The Prime Minister is clinging on, but his days are numbered.