Boris Johnson's premiership hangs by a thread tonight after Health Secretary Sajid Javid and Chancellor Rishi Sunak dramatically quit in the wake of the Chris Pincher scandal.
As the Prime Minister's authority drains away, speculation is mounting that a leadership challenge could be on the cards within days as a flurry of Tory MPs who previously backed the PM called for him to stand down.
Meanwhile, Labour leader Keir Starmer has said Britain needs a "fresh start" as he backed calls for a snap general election.
He told broadcasters: “He is unfit to be Prime Minister. He is not fit to govern the country.
“That is dawning on many people across the Conservative party, but they have to reflect on that, that they have backed him for months and months and months."
So, who could replace beleaguered Boris Johnson? Here are the runners and riders.
Jeremy Hunt
The frontrunner, 55, was the last candidate standing against Boris Johnson in 2019. This time he spent months in a "will he, won't he" tussle before coming out on the day of the vote.
He said "I will be voting for change" because otherwise the Tories "are set to lose the next general election". He added: "We are not giving the British people the leadership they deserve. We are not offering the integrity, competence and vision necessary."
Britain's longest-serving Health Secretary sparked fury on the left for pushing through junior doctor contracts that were deemed dangerous. But in Tory eyes he is near the moderate, internationalist centre of the party, serving in a string of top roles, backing Remain and now chairing the Health Committee.
An MP since 2005, he was educated at £41,000-a-year public school Charterhouse and is a millionaire after founding the educational firm Hotcourses in 1990.
He and his Chinese-born wife, who he mistakenly said was Japanese in a bizarre 2018 gaffe while Foreign Secretary, have spent millions on a portfolio of luxury flats. He broke ethics rules by failing to declare his stake for six months.
Liz Truss
Britain's first female Foreign Secretary has been on a journey since she branded the level of cheese imports a "disgrace" while a Remainer Environment Secretary in 2014.
Cast back even further and she was born into a lefty family, chanting 'Maggie Maggie Maggie, out out out' with her mother and later protesting Tory policy as a Lib Dem activist.
The comprehensive-schooled MP has since become a darling of some sections of the Tory right, boasting the benefits of Brexit while International Trade Secretary and failing to defend judges who were branded "enemies of the people" when she was Justice Secretary.
She has never confirmed she is running for leadership but it's a running joke in Westminster. She poses for carefully-choreographed social media posts, including jogging on the Brooklyn Bridge and posing in a tank like Margaret Thatcher.
The 46-year-old became an MP in 2010 after working at Shell, Cable and Wireless, and then as deputy director of the Reform think tank. She has had to defend Tory tax rises but spoke out against a windfall tax on oil giants and insists she is a low-tax Tory.
Tom Tugendhat
The Tory chairman of the Foreign Affairs Committee, 48, has only been an MP for seven years but was the first to confirm he’d throw his hat in the ring.
The centre-right former Remainer has been a vocal critic of Boris Johnson's foreign policy - such as on Russian sanctions and the botched withdrawal from Afghanistan - and said recently he had made his position "clear to those who need to hear it".
The privately-educated son of a High Court judge has dual citizenship with his France where his wife is a judge, speaks Arabic, and voted remain in the 2016 Brexit debate. His family own a forest in Essone, near Versailles.
He served in Iraq as an intelligence officer with the Royal Marines and ran the central region - Baghdad and the surrounding cities - in 2003. Later he became advisor to the governor of Afghanistan's Helmand Province.
Rishi Sunak
The slick 42-year-old Chancellor nicknamed 'Dishy Rishi' by his admirers shot up the rankings since becoming an MP seven years ago. He was long seen as the frontrunner to succeed Boris Johnson as Britain's first PM of Asian descent.
But the former investment firm founder has slipped down the rankings after a serious of "out-of-touch" gaffes as the cost of living crisis bites.
It emerged his wife Askhata Murty, with whom he's 222nd on the Sunday Times Rich List with a combined £730m fortune, was paying £30,000 a year to use her non-dom status not to pay UK tax on her overseas income. She later U-turned.
A fan of posed photos on Instagram, the four-car-owner was widely mocked for promoting a temporary fuel duty cut using someone else's car. Cameras also captured the embarrassing moment he struggled to use his bank card to pay.
Mr Sunak and his wife, daughter of an Indian billionaire, have been building a tennis court, swimming pool and gym at their gated Grade II-listed manor in North Yorkshire. He begins his days with a Britney Spears-soundtracked workout on his £1,750 Peloton exercise bike, posed in £95 'slider' shoes in a photo op, and sips from a £180 Bluetooth 'smart mug'.
Despite his image, some moderate Tories still believed he was the best candidate - especially if it was a choice between him or Liz Truss. But it would be difficult for him to run when he, too, has been fined by police over Partygate.
Penny Mordaunt
Back in government since February 2020, the 49-year-old Trade Minister has kept her head down but is widely thought to hold ambitions for leadership.
The Royal Navy reservist has trodden a diplomatic path, supporting Brexit while opposing bids to oust Theresa May in 2018. But she also has a sense of humour - she took part in a reality TV show Splash and used the word “cock” six times in a Commons debate as part of a game with fellow reservists.
Born to an ex-paratrooper, named after a Navy ship and related to both Angela Lansbury and Labour's first chancellor Philip Snowden, she was educated at a Catholic school, a drama school and Reading University.
Since becoming an MP in 2010 she has worked in a string of top jobs including Defence Secretary but was sacked from the Cabinet by Boris Johnson - only to be brought back at a more junior rank.
Ben Wallace
The 52-year-old Defence Secretary, an MP since 2005, is respected by many Tories for his no-nonsense style - including weeping in an interview last year over the withdrawal from Afghanistan and hitting back at Putin's threats over Ukraine.
But his blunt manner could also cost him some advancement, such as in 2019 when No10 slapped him down for being caught on camera making remarks about Boris Johnson's prorogation of parliament.
The privately-schooled son of a soldier attended Sandhurst and served in Germany, Cyprus, Belize and Northern Ireland before entering politics in the early 2000s, including as an aide to Ken Clarke.
Nadhim Zahawi
The 55-year-old had a remarkable life story before being named Vaccines Minister during Covid, then Education Secretary.
His Kurdish parents fled Baghdad when he was nine and he was educated at a West London comprehensive, then a private school before attending UCL and building up a lucrative business career.
He co-founded the leading pollster YouGov before being elected to Parliament in 2010, and had a lucrative career with the oil industry, being paid more than £1,000 an hour by Gulf Keystone Petroleum before he took a ministerial job.
Last year the Mirror disclosed he, his wife and their companies had built a £100m property portfolio. In 2013 he promised to repay a bill for power at his stables which was funded by taxpayers.
Sajid Javid
The Health Secretary was one of 10 leadership challengers in 2019. Boris Johnson made him Chancellor but the relationship quickly soured, with Mr Javid resigning in February 2020 after he was told to fire his advisers.
He was on the back benches for most of the pandemic before returning to the Cabinet as Health Secretary.
The 52-year-old MP since 2010 rose through the ranks after being close to ex-Chancellor George Osborne. He came under fire in 2015 after the steel sector was battered by thousands of job losses but he jetted off on holiday to Australia with his daughter.
His father, Abdul, was a bus driver who arrived in the country in 1961 with £1 in his pocket. He went to a comprehensive school in Bristol before studying economics and politics at Exeter University. He once hit a classmate who called him a “p**i”, and was told in his first interview for a City job that his face “wasn’t going to fit in there”.
But he later carved out a high-flying career in finance, working as a managing director at Deutsche Bank. The free marketeer apologised in July 2021 for saying it was time to stop "cowering" from Covid.
Michael Gove
Boris Johnson's ally turned rival has held a string of cabinet posts and is currently overseeing the PM's flagship levelling up agenda.
But the PM's allies branded him an "amazing s***" in 2016 when he detonated Mr Johnson's leadership bid after the Brexit vote. After saying he was unlikely to, he then stood again in 2019 before losing out at the final ballot to Jeremy Hunt and Mr Johnson.
During his campaign he admitted to taking cocaine when he was in his twenties - despite criticising middle-class drug users.
The 54-year-old's personal life came under the spotlight last year when he announced his divorce from columnist wife Sarah Vine, and was later spotted throwing shapes in an Aberdeen nightclub. Despite this he's broadly seen as a slick - if slippery - messenger for whichever government rules the day.
Could he make it a third run at the top job? Allies insist he's said he wouldn't run again a few times, but that hasn't stopped him before.
Dominic Raab
The Deputy Prime Minister, 48, made it to the third round of the 2019 leadership contest after rising through the ranks as a Brexiteer.
The grammar school-educated former human rights lawyer, a karate black belt, became an MP in a Lib Dem target seat in 2010 and previously served as Brexit Secretary and Justice Secretary.
He gained praise for deputising for Mr Johnson when the PM was hospitalised with Covid in 2020. But he was moved from being Foreign Secretary after the disastrous withdrawal from Afghanistan, while he holidayed in Crete insisting the "sea was closed".
The right-winger once branded feminists "obnoxious bigots" and put out a pamphlet in 2011 that suggested exempting small firms from minimum wage laws for workers under 21.
He sparked fury in 2017 by saying most food bank users are not "languishing in poverty". When a disability activist told him "people are dying" under Tory austerity, he described her calls for cash as a "childish wish list".
While he could yet head the government again, it might only be as a stand-in if a temporary PM is needed. Since his 2019 run, other right-wingers have come to the fore as potential candidates and he'd face stiff competition.
Mark Harper
The 52-year-old MP since 2005 had an abortive leadership run in 2019 in which the most exciting moment was saying he'd back the big cat in a fight between a lion and a bear.
Since then the Covid Recovery Group co-chief become a darling of lockdown rebels and one of the ringleaders among right-leaning Tory backbenchers who are discontented with the PM's leadership.
But he's told friends he is unlikely to throw his hat in the ring.
Priti Patel
To her admirers the 50-year-old MP since 2010 is the ultimate Tory success story, inspired into politics by Margaret Thatcher after being raised by a Ugandan-Indian family in London and moving from PR into politics.
To her critics she is a hardline right-winger who has led repeated attacks on refugees and the right to protest while Home Secretary.
Even then, her failure to stem the numbers of desperate people crossing the Channel in small boats - including with a legally contentious plan to force them to Rwanda - could count against her with Tory MPs.
She was forced out as Theresa May's Trade Secretary in 2017 for holding off-the-books meetings during a holiday to Israel, which it was claimed broke the Ministerial Code. She was accused again of breaking the Code over bullying claims but exonerated by Boris Johnson, who overturned an ethics advisor's recommendation.
The Home Secretary showed her loyalty to Boris Johnson by chivvying MPs on a Tory WhatsApp group that they needed to get behind him. But she is said to be considering a leadership bid this time around.
