Meet the challengers

David Miliband, nicknamed 'Brains' by Tony Blair's staff for his formidable intellect, is a tech-savvy policy wonk who won a strong reputation in Washington as he served as Britain's foreign policy chief. At 44, he is drawn from the same generation as Cameron and Clegg, both aged 43, and seen by many as the most viable proposition to restore the Labour Party to prominence.

He already has one ringing endorsement from overseas - last year Clinton described Miliband to American Vogue as "so vibrant, vital, attractive, (and) smart".

Blair could also pledge his support, though Miliband has attempted to open up some distance from his former boss, suggesting Britain would never have backed the 2003 US-invasion of Iraq if it knew weapons of mass destruction would not be found. Blair said recently that toppling Saddam justified the mission in any event.

But Miliband's greatest challenger may be one of the men he knows better than any other, his 40-year-old brother Ed Miliband.

The brothers, whose father Ralph was a respected Marxist theorist, and mother Marion Kozak was a leftist academic, have similar political outlooks, though Ed is seen as closer to his party's left-wing and was responsible for drafting Labour's election manifesto.

As Britain's former energy and climate change secretary, Ed Miliband took a lead role in negotiating at the December talks in Copenhagen aimed at reaching a global pact to reduce greenhouse gas emissions.

"They're awfully close, from what I understand," said James Cronin, a professor of British history at Boston College. A race between the two, he said, would be "fascinating".

New hairstyle

In north London, hairdresser Conchita Cooper told David Miliband she had a tip to take an advantage over his sibling, suggesting he should consider a new style for his "very bushy" hair.

Hilton said it's understandable two men who shared a childhood steeped in politics would both run to lead their party.

Some see the leadership race as a contest by proxy of the showdown Blair and Brown managed to avoid, seeing Miliband as Blair's heir, and combative ex-education secretary Ed Balls as Brown's favoured candidate.

Balls, 43, struggled to hold his House of Commons seat at the election, but is likely to join the leadership race. Noted for his brusque style, the ex-economic reporter has already led Labour's attacks on Cameron and Clegg's coalition.

"Ed Balls may have some strong links with unionists, but he's got quite a lot of work to do to translate that into votes," Katwala said.

Balls said yesterday his party wanted "a proper debate and I'm going to take that very seriously".

Labour lawmaker Michael Dugher said yesterday the contest is almost certain to end up "David Miliband versus Ed Balls versus Ed Miliband."

Husband-wife face-off?

Just as David Miliband's brother is likely to run, so too may Balls' wife Yvette Cooper, a former Cabinet minister and one of few women touted as an alternative to replace Brown.

Though she said on Wednesday she would not put herself "forward for the top job right now", some expect her to be pressed to become a candidate.

Respected leftist legislator Jon Cruddas, 48, who refused a job in Brown's Cabinet, is also expected to join the contest.

Under Labour's rulebook, Brown's successor will be chosen by a vote of an electoral college of House of Commons legislators, the party's European lawmakers, grass-roots activists and affiliated organisations, including labour unions. No ballot is yet planned, but the result is expected to be announced at the party's annual convention in September.

The elder Miliband promised to spare one party member from making a difficult choice.

"My mum, who's a member of the Labour Party, will abstain in this vote," he said.