UK Prime Minister Gordon Brown said on 10 May he would step aside this year, sacrificing himself to try to give his Labour Party a chance of forming a government with the smaller Liberal Democrats.
"I have no desire to stay in my position longer than is needed to ensure the path to economic growth is assured and the process of political reform we have agreed moves forward quickly," Brown said.
"As leader of my party I must accept that that [the election result] is a judgement on me. I therefore intend to ask the Labour Party to set in train the processes needed for its own leadership election," he added.
Brown did not give a precise timeframe for his departure, but said he hoped it would be done by the time of the Labour Party conference, which is scheduled for late September. Earlier, Liberal Democrat legislators said they were seeking clarification from the party's negotiators about details of a possible deal with the Conservatives.
"Although we are very, very conscious of the need to make these decisions quickly, and that's a clear decision of the parliamentary party today, we also want to make sure that we get these matters right," said Lib Dem legislator David Laws.
Conservative and Lib Dem negotiators said earlier they made progress at talks to reach a power-sharing deal, although others called for caution on how quickly a deal could be clinched.
The rules for changing the leader
The rules governing the election of a Labour leader are complicated and depend on whether there is a vacancy or not.
When the party is in government and a vacancy arises, the cabinet will, after consultation with the party's National Executive Committee, appoint one of its members as interim leader until a ballot can be held.
If the party is in opposition, the deputy leader automatically becomes temporary leader.
To take part in the leadership election, any potential candidate must be supported by 12.5% of the members of the Parliamentary Labour Party (PLP).
The voting is split equally three ways between Labour MPs and the Labour Members of the European Parliament, party members, and members of affiliated trade unions who have not opted out of paying a political levy.
The votes of each nominee in each section are then calculated as a percentage of the total votes cast in that section.
The ballot must take place at such a time which means the results can be declared at the annual party conference or at a special leadership election conference.
If any candidate receives a majority of votes, they are declared the leader. If not, the last place contender drops out and their second preferences reallocated, until someone passes the 50% figure.
Who could take over?
Here are some details on likely contenders.
- Born in July 1965, Miliband was nicknamed "Brains" by Tony Blair's former spokesman and has been foreign secretary since 2006, the youngest in that post since David Owen in 1977.
- After Blair stood down as prime minister in 2007, Miliband was touted as a possible challenger to Brown for the top job. He was also briefly linked to a leadership challenge in 2008 before dismissing the media reports.
- He is the bookmakers' clear favorite to replace Brown.
- Moved from the health ministry to the more powerful interior ministry in June 2009. A guitar-playing former postman, Johnson, born in May 1950, is portrayed as a man of the people who could help Labor reconnect with its working class roots.
- Johnson's easy style impresses supporters, but critics say he is vague on policy, particularly on the economy.
- He was orphaned at the age of 12 and brought up by his elder sister in a state-owned flat in London. He worked as a supermarket shelf-stacker before becoming a trade union leader.
- Brown's former right-hand man at the Treasury, Balls was appointed Secretary of State for Children, Schools and Families in June 2007. He is firmly on the left of the party.
- Born in February 1967, Balls was educated at Oxford and Harvard and worked as a leader writer and columnist at the Financial Times. He is married to Yvette Cooper, the work and pensions secretary.
- Younger brother of David, Ed was born in December 1969 and is seen as one of the rising stars in the party. Supporters say he has a more relaxed presentational style than David and that would make him the best candidate to deal with slick Conservative leader David Cameron.
- He was named Energy and Climate Change Secretary in 2008.
- Born in November 1953, the Edinburgh Central MP attended the private Loretto School on the outskirts of Edinburgh, before going on to study law at Aberdeen University.
- Darling is a former left-winger who moved to the center ground when Blair revamped Labour during its long years in opposition. He took over as finance minister when Brown became prime minister in 2007
- Born in July 1950, Harman was educated at St. Pauls, one of Britain's elite girls' schools. She worked as a civil liberties lawyer before entering parliament in 1982.
- The leader of the lower house and deputy Labour leader has close ties to Brown. Supporters describe her as a tenacious workaholic with a strong record on sexual equality and workers' rights. Critics nicknamed her "Hattie Harperson" for her political correctness.
- Mandelson, born in October 1953, was one of the architects of former prime minister Tony Blair's "New Labour" project, which moved the Labour Party to the political center, enabling it to win a landslide election victory in 1997.
- Currently First Secretary of State, Secretary of State for Business, Innovation and Skills, he served as MP for Hartlepool for 12 years from 1992, before vacating his seat to become a European commissioner between 2004 and 2008.
- Mandelson sits in the unelected House of Lords, which would prove an obstacle to him becoming prime minister.
- Famous for his tactical skills as a backroom operator, Mandelson has long been nicknamed the "Prince of Darkness".
- No ministerial experience, on the left of the party but highly regarded by moderates too. Dubbed the "Thinking man's street fighter" in an article by the Economist magazine.
- Cruddas, born in April 1962, represents a constituency in east London where he has gained kudos for campaigning against the far-right British National Party which has a large support base in the area.
(EURACTIV with Reuters.)