The new leader of the United Kingdom's main opposition Labour Party will be announced on April 4 at a special conference.

The three-month contest to replace outgoing leader Jeremy Corbyn and Tom Watson, the former deputy leader, comes after Labour lost the December 12 election, in its worst showing since 1935.

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Nominations to lead the party will close on January 13. A postal ballot of members will run from February 21 to April 2.

"We are by far the largest political party in the UK," a Labour spokeswoman said.

"We want as many of our members and supporters to take part [as possible], so it has been designed to be open, fair and democratic."

According to a government website, as of July 2019, Labour had 485,000 members compared with the ruling Conservative Party, which had 180,000.

Who has declared candidacy so far?

So far, six candidates have announced they intend to stand for the leadership - frontbenchers Sir Keir Starmer, Emily Thornberry, Rebecca Long-Bailey and Clive Lewis, and backbenchers Jess Phillips and Lisa Nandy.

Sir Keir Starmer

The shadow Brexit secretary and former director of public prosecutions is Labour members' favourite to win the leadership, according to a recent YouGov poll.

He is viewed as more of a centrist than his main rival, Long-Bailey.

But his campaign has seen him play up his left-wing credentials, highlighting his work as a lawyer supporting trade unions and poll tax protesters.

He believes the party should not "oversteer" to the right in the wake of the election defeat, largely blamed on Corbyn's left-wing agenda, which some criticised as too "radical".

Starmer has been the MP for Holborn and St Pancras since 2015 and was instrumental in getting the party to back a second Brexit referendum - although he acknowledged that the scale of the election defeat meant the issue was now settled.

Emily Thornberry

The shadow foreign secretary is another pro-Remain MP who, like Starmer, was out of the limelight during the general election campaign.

Thornberry, who has been criticised for "leniency" towards Syria's President Bashar al-Assad, 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.

She was first elected as MP for Islington South and Finsbury in 2005.

Rebecca Long-Bailey

The shadow business secretary is highly rated by the current Labour leadership, leading to claims that she would be the "continuity candidate", keeping Corbyn's leftist flame alive.

The Salford and Eccles MP grew up in the shadow of football team Manchester United's Old Trafford stadium and watched her father worry about job losses as a docker and trade union representative.

She has the support of party chairman Ian Lavery, who had reportedly been considering a leadership bid of his own, and shadow education secretary Angela Rayner, her friend and flatmate, who is in the running for deputy leader.

Clive Lewis

The shadow Treasury minister, who was a pro-Remain MP, has promised to transform the party and offered a "vision for the country ... of warmth and energy and of us all being in it together".

He has backed a shift to proportional representation and reform of the House of Lords, and suggested that Labour should "reach out to every other progressive force in the country - parties, campaigns and movements - for the biggest conversation possible about how, together, we can change our country for the better".

A former BBC journalist and Army reservist who served in Afghanistan, Lewis has been MP for Norwich South since 2015.

Jess Phillips

The Birmingham Yardley MP has a high profile despite never having held a frontbench role.

Her campaign video details how she got involved in community activism in the Birmingham street where she grew up and raised her family.

Phillips told Corbyn in 2015: "You are hurting us more than you are helping us, I won't knife you in the back, I'll knife you in the front."

She has warned Labour would be in "big trouble" if it fails to win back the trust of its working-class base.

Lisa Nandy

The Wigan MP and former shadow cabinet minister launched the Centre For Towns think-tank in 2017 - something that could give her an advantage in understanding why voters in former industrial Labour heartlands switched to the Conservatives in the December election.

She said too many people "no longer feel they have a voice in our national story" and did not believe that politicians were interested in what they had to say.

Before being elected in 2010, Nandy worked for the youth homelessness charity Centrepoint and The Children's Society.