THE strangest thing about the Labour leadership race isn’t the fact that the candidates are mostly a bunch of eerily similar middle-class men or even that two of them are brothers. It’s how close it is going to be.

As the contest enters its final days before an announcement on September 25, what once looked like a one-horse race has broken into fraternal struggle – with scarcely space for a ballot paper between them.

On Sunday, a YouGov poll showed just how tight it was: frontrunner and bookmakers’ favourite David had suddenly and surprisingly fallen behind his younger brother Ed – albeit by a tight 51 to 49 percent split.

Barely 24 hours before that turnaround, the elder Miliband was looking quite at home at his campaign headquarters in Westminster.

In lumberjack shirt and jeans with a broad smile, he had that relaxed air of leadership material: that mixture of authority, humility and casual familiarity.

His two young sons and wife Louise were with him, closely clutching accessories for a day in the park. This wasn’t photo-opp politics (David politely requested the boys be left out of any pictures), but a man who is now at home with the work at hand and vying to become future leader and eventually Prime Minister.

You got the sense that, even if he was aware of the upcoming shift in momentum, it would be unlikely Miliband senior would carry himself any differently.

“Saturdays are pretty sacrosanct,” he explained.

When you consider the toll the four-month-long campaign must have had on him, you can understand why.

In the three years since he refused to stand against Gordon Brown, he has been the man most talked about in connection with the leadership.

At that point, and again a year later when he refused to lead another coup against the Prime Minister, it is widely accepted that Miliband put a desire to keep the party intact before his own political career.

Then, as the moment finally came for him to realise his ambition, his younger sibling seemed to come from nowhere and decided he wanted a bite too.

Although there are no signs of a family feud – he asks with a grin if I have already met “brother Ed” – the shock for the elder Miliband must have been grave.

Yet David, who calls himself the “unity candidate”, remains resolutely dedicated to the party above all else – even what some people see as a brother’s betrayal.

“All along, we’ve had the strategy to beat the Tories – not just the opponents – my friends who are now my short-term rivals,” he smiled. “It is about becoming a community campaign organisation and the real issue is how to beat the Tories.

“Unity is not just left to right, it’s from top to bottom and it’s geographic. I’ve got more Scottish MPs than anyone supporting me. My concept is Team Labour. If we’re not a team than we’ve had it. We need to stick together.”

How much David will stick around if he fails to win the nomination is another question entirely.

When I ask him if he would be happy to work with any of the other candidates as leader, he responds “of course” but his voice betrays his reluctance.

The loss of David Miliband from frontline politics would be a serious blow to Labour’s electoral chances.

In polls of the public at large, David is consistently the candidate the public would choose as opposition leader.

Even David Cameron has been exposed for wanting “Red” Ed Miliband to prevail over David in the hope that the younger brother, with all his support for unions and redistributive taxation, would be too left-leaning for current centrist politics.

“The Conservatives don’t want a strong united mainstream Labour party, which is what I stand for,” David said.

“Historically, like in 1931 and 1979 when Labour lost, it’s been out of power for a long time. One reason I am standing is that I think I’ve got the best chance of bucking that trend.”

This is where David has been labelled a Blairite: commentators compare Ed’s strategy of wooing core voters and union support to his brother’s more measured acknowledgement of the importance of appealing to the southern middle-classes: “We’ve got to make sure, in the areas that are becoming no-go areas, we get a presence again,” he said.

“We are the only national party, we’re in Scotland and Wales. We’ve got to make sure that all over England we’ve got a strong Labour party too.”

On issues raked up by his brother’s campaign team who have been all too happy to push him closer to Blair, David refuses to be drawn.

“Iraq was a big decision in 2003 and I am talking about Britain in 2015,” he says.

It is credit to the ability of Junior Miliband’s campaign – if not its dignity – that they have also managed to build on pre-conceptions of David’s personality.

Some commentators say Ed “speaks human” while David’s obsession is with all things political; Ed’s childhood love of Dallas is contrasted with David’s love of debate and discussion with their late father Ralph Miliband, a renowned socialist.

In person though, this is no rigid political geek.

In fact, David carries himself much better than his younger brother: There is no awkward gait, he doesn’t look out of his depth and actually seems much more personable.

This, after all, is a man whose charisma was enough to make Hillary Clinton swoon.

Then there’s his experience: since entering parliament in 2001 as MP for South Shields, he has held ministerial roles in departments from education to environment, ultimately becoming one of the youngest foreign secretaries in Westminster for 30 years.

His grounding in adversarial politics is what is lacking in his brother. It is that which perhaps makes the younger Miliband seem slightly unsure of himself.

Whatever it is, David knows how to run a dignified campaign. There’s been no mud slinging, no bad-mouthing the work of previous Labour administrations but a desire to move away from what he sees as negative politics.

“It is really important that there is a positive choice,” he said. “You can’t beat something with nothing. We’ve got to oppose things and expose them but we’ve also got to be able to propose as well.

“There has got to be an alternative and we can’t be a fighting opposition only. We’ve got to be able to be a government.”

The concern is that, while he has the edge with voters, members may eschew the pragmatic choice.

Lengthy opposition may be the historical inevitability of a party who are unable to let the ghosts of Old and New Labour lie side by side rather than swinging like a pendulum between the two.

David wants them to choose him as a figure beyond both movements.

“I talk about a moral economy where there is fairness from top to bottom,” he said. “I talk about the redistribution of power so that local councils and communities are stronger. I talk about tackling inequalities of opportunity, and issues of education and health are central to that.

“It says on our party cards that we believe in power of opportunity for the many not the few – that’s a pretty good definition of what I am about.”

Whether it’s David’s commitment to fairness which meant he didn’t block his brother from standing, we may never know, but if it means political opportunity is knocked out of his hands for good, Labour may have a long wait in the wings.