As Labour deals with a devastating defeat at the general election, here is a look at who could be in the race to replace Jeremy Corbyn as party leader.
The shadow chancellor played a prominent role throughout the general election campaign, but appears to have ruled himself out as a future leader.
On Thursday night, Mr McDonnell said he will not serve “either as a temporary or a permanent” leader of the Labour Party if Mr Corbyn were to resign.
Back in October, Mr McDonnell said he “can’t see” how he or close ally Mr Corbyn could continue to lead the party if they failed to win power after the next general election.
Ladbrokes made him a 25/1 outsider to take the top job.
The shadow foreign secretary has deputised for Mr Corbyn at prime minister's Questions and has represented the Labour Party on various overseas visits.
Ms Thornberry, who campaigned for Remain in the 2016 Brexit referendum, joined the party when she was 17 and was motivated by her experiences being raised by her mother, a single parent living on a council estate, according to her website.
She was first elected as MP for Islington South and Finsbury on May 5th 2005.
Ladbrokes and Coral gave odds of 12/1 for Ms Thornberry.
The shadow Brexit secretary was a human rights lawyer before becoming an MP, and co-founded Doughty Street Chambers in 1990.
He worked as human rights adviser to the Policing Board in Northern Ireland, monitoring compliance of the Police Service of Northern Ireland (PSNI) with the Human Rights Act, and in 2008 he was appointed Director of Public Prosecutions (DPP) and Head of the Crown Prosecution Service for England and Wales.
Sir Keir was elected as Labour MP for Holborn & St Pancras in May 2015.
Ladbrokes and Coral said Sir Keir was favourite for the post, offering odds of 5/2 and 2/1 respectively.
Mr McDonnell named shadow education secretary Ms Rayner as a possible successor to Mr Corbyn in an interview with former Labour spin doctor Alastair Campbell for GQ magazine in October, saying whoever comes after Mr Corbyn "has got to be a woman".
Ms Rayner was brought up on a council estate and left her local comprehensive at 16 with no qualifications and pregnant, after being told she would “never amount to anything”, according to her website. It adds that in 2015 she became the first woman MP in the 180-year history of her Ashton-under-Lyne constituency.
Her web page also says she rose through the ranks of the trade union movement to become the most senior elected official of Unison in the North West.
She was made fourth favourite at 7/1 by both Ladbrokes and Coral.
The shadow business secretary grew up by Old Trafford football ground in Manchester and began her working life serving at the counter of a pawn shop, according to her website.
She has also worked in call centres, a furniture factory, and as a postwoman before eventually studying to become a solicitor, her online biography adds, while she describes herself as a “proud Socialist” in her Twitter profile.
In 2015, she was elected as MP for Salford and Eccles.
Both Ladbrokes and Coral offered odds of 4/1, making her second favourite.
The current Mayor of London was MP for Tooting from 2005 until 2016, and if he fancied a return to parliamentary politics he could put himself in the running for leader.
But he is expected to contest the 2020 mayoral race.
Mr Khan has served as a local councillor and was transport secretary in the last Labour government.
During his campaign to become London mayor, he frequently pointed out that his father was a bus driver in the capital.
Ms Cooper has been an MP since 1997 and has held positions including chief secretary to the Treasury and secretary of state for work and pensions when Labour was in government.
More recently, Ms Cooper has been on a number of committees including the Home Affairs Committee, where as chair she has conducted forensic questioning.
Ms Cooper, who is married to Ed Balls, is a prominent Commons figure and is popular among MPs.
In an echo of her third place finish in the 2015 leadership election, she is said to be third favourite at 5/1 by both Coral and Ladbrokes.
The outspoken Birmingham Yardley MP won in her third successive election, having first been elected to Parliament in 2015 and re-elected in 2017.
In her victory speech, she made clear she believed her party needed “structural change”, adding: “The reality is that the Labour Party has got to do a huge amount more than just think that getting rid of one man ... will just simply make it OK.”
Before being elected, Ms Phillips worked for Women's Aid, supporting female victims of domestic abuse.
Ladbrokes said it had slashed her odds from 20/1 to 8/1, while Coral offered the same price. –PA