The turmoil in Britain's Labour Party worsened after its MPs backed a motion of no confidence in their leader, Jeremy Corbyn, by 172 to 40.
Corbyn rejected calls to quit, but there's now little to stop disaffected members of Parliament launching a formal challenge to his leadership. Corbyn's deputy, Tom Watson, and former foreign policy spokesman, Hilary Benn, have ruled themselves out of standing.
So who might take over? Here's a look at the main candidates. And with a general election possible later this year, one of them might just be prime minister before Christmas.
1 JEREMY CORBYN
Who: The incumbent
The Labour leader is elected by the party as a whole, and many rank-and-file members still back Corbyn, so it's very possible they will choose to re-elect the man MPs are currently revolting against.
After decades as an MP better known for rebelling against the Labour leadership than toeing the party line, Corbyn, 67, was unexpectedly propelled into the top job last year. His offer of "straight talking, honest politics" struck a chord with party members and supporters.
Corbyn won an overwhelming mandate in the country, but only 10 per cent of Labour MPs in the House of Commons voted for him. He has struggled to assert any authority over MPs, who have accused him of lacking vision, campaigning skills and the ability to reach out to voters in Labour heartlands, many of whom are being drawn to the UK Independence Party. Critics also say he has failed to successfully exploit splits in the governing Conservative Party.
His supporters, who gathered in their thousands outside Parliament this week to show their support, say Corbyn can reach voters disillusioned with politics. But his lackluster performance in the European Union referendum campaign left many doubting his ability to successfully lead Labour into a general election.
2 ANGELA EAGLE
Who: The favorite.
One of a pair of twin sisters at the top of the Labour Party, Angela Eagle was a Treasury minister under Gordon Brown and rose to be the most senior woman in the party before her resignation from Corbyn's shadow cabinet. She has been in the House of Commons since 1992.
An assured performer in Parliament, Eagle, 55, was chosen to represent the Remain side in one of the television debates during the referendum campaign. She chaired Labour's policy forum before the last election and lost out to Watson in last year's deputy leadership contest.
An international-level chess player as a child, Eagle worked for the Confederation of British Industry and a health-care workers' union before entering Parliament. If she were to win, Eagle would be the first openly gay MP to lead a major UK party nationally.
3 LISA NANDY
Who: The straight-talker.
Lisa Nandy, 36, was elected to Parliament in 2010 after almost a decade of working in the voluntary sector for homelessness and children's charities. Her straight-talking approach has led her to be installed as one of the favourites with bookmakers in the event of leadership election.
Touted as a candidate initially last year, the representative for Wigan in northwest England chose not to run following the recent birth of her son. Nandy served in Corbyn's shadow Cabinet as energy spokeswoman until she quit this week, saying in a joint statement with fellow MP Owen Smith that she had lost confidence in Corbyn's ability to lead and unite the party's left and right wings.
Born in Manchester, she earned a politics degree from Newcastle University before a stint working for a Labour MP preceded her charity work. She served on Parliament's Education Committee and then acted as Labour's spokeswoman for children and for civil society under Ed Miliband, before taking the energy brief when Corbyn assumed the leadership.
4 DAN JARVIS
Who: The military man.
Jarvis, 43, turned down calls to run for the Labour leadership last year, despite suggestions that he'd be the candidate the Conservatives would fear most. A former company commander in the Parachute Regiment who served in the Balkans, Afghanistan, Iraq, and Sierra Leone, Jarvis's military background makes him stand out from the pack.
Seen as a Westminster outsider, the MP for the northern district of Barnsley since 2011 hinted he might quit the party earlier this year if it ditched its commitment to Britain's nuclear deterrent as Corbyn has espoused.
He served as a shadow justice and culture spokesman under Miliband but didn't join Corbyn's team. Viewed as a moderate and a Blairite, Jarvis has kept a low profile in the recent coup attempt.