Ed Miliband has declared he will challenge his brother and run for leader of the Labour Party.

The former energy secretary, in a speech to the Fabian Society in London, said: "I have talked to my family and friends I have decided to stand to be leader of the Labour Party."

Launching his campaign to applause, Mr Miliband called for a "fraternal" contest for all candidates who put their names forward, including his brother David.

He said: "My message to the British people is, we will learn from our mistakes, we will be part of your values again, we will be part of your community again and we will work with you to build the kind of country we want to see.

"And my message to our party is this: we have to use this leadership campaign as a first step on the road back to power because that is where we should be as a political party.

"It involves facing up to uncomfortable truths.

"I think it should be a fraternal contest, and not just in terms of myself and David, but all the candidates at this election."

Ed Miliband added that Labour had "lost touch with the values that made us a progressive force in politics."

He called on Labour members to "face up to the scale of defeat" in the general election and use the time in opposition to "renew".

Earlier, he joked that he could reveal the answer to the question of which brother his mother would choose to support.

"I do want you to be the first to know the answer to this because I think I can say that I am confident that, on the basis of her position on the political spectrum and on the basis of the runners and riders, that her candidate for the Labour leadership will be Jon Cruddas," he quipped.

David Miliband is the only other candidate so far to have thrown his hat into the ring for the Labour leadership since Gordon Brown stood down on Tuesday.

Announcing his candidacy on Wednesday, former foreign secretary David Miliband said that he would set out on a "conversation" tour of the UK to find out from voters why they turned away from Labour.

He will formally launch his campaign in his South Shields constituency on Monday.

Meanwhile, former children's secretary Ed Balls has told Sky News that he would "think hard" and consult his local party in Morley and Outwood before deciding whether or not to stand for the leadership.

Mr Balls insisted he would back whoever emerged as leader: "Whether I stand or not, whoever wins I will back them 100% because that is the only way for us to win," he added.