IT wasn’t the Iraq War jibe that most clearly betrayed David Miliband’s bitterness about his brother’s leadership victory – but his reaction to a joke about Forrest Gump a few moments earlier.

Ed Miliband won a few laughs when he questioned his alleged resemblance to the Tom Hanks character in the 1994 Oscar-winning film, telling his audience: “Not so much.”

An innocent joke, surely? Not to big brother David, whose expression – the TV news revealed later – was close to murderous in the front row below.

Last month, Miliband senior denied his aides had turned nasty by comparing his brother to the film’s friendly idiot, known for his banal catchphrases, insisting: “No one on my campaign says that. No one.”

On Tuesday, I saw a mix of contempt and near-loathing in David’s eyes, so angry was he that Ed had chosen to bring up this sensitive spat in his showpiece conference speech.

At that moment I knew the Shadow Foreign Secretary would walk away from Labour’s top team – and that the decision had little to do with fears that media fixation on the Miliband melodrama will damage the party.

No, I saw a man who – even knowing every TV camera was fixed on him – was unable to control his shattered emotions at the moment of his brother’s triumph.

And if the pain of defeat triggered such an extreme reaction to a joke about Forrest Gump, then what hope could there possibly be of reconciliation when the Shadow Cabinet gets around to discussing the serious stuff?

This observation is not to meant to blame David Miliband for his inability to accept his brother destroying his political career, because he would hardly be alone in that.

From Cain slaying Abel, to Noel breaking up Oasis to escape Liam, to Frasier Crane’s fury when Niles beats him to become corkmaster of their local wine club, we all know about sibling rivalry.

At a conference dinner, Ed Miliband apparently joked that he was Britain’s equivalent of North Korea’s Kim Jong-un – a younger son who leapfrogs into leadership.

As a younger brother – one who followed his sibling into journalism, in the way Ed followed David into politics – I struggle to imagine myself fighting him for a top job I knew he coveted above all else.

Intriguingly, one of the region’s MPs told me he was convinced this was a new North- South divide, believing a Northern bloke would never do the dirty on big brother – while a posh Southerner would happily eat him for breakfast.

I have no idea if that’s true, but I do know David is not the only Miliband eager for a split. Whatever he says in public, Ed must know that his brother’s devastation leaves no alternative.

LITTLE sign of Blairite revival on the conference fringe where Tony’s celebrated memoirs, A Journey, were reported to have shifted just four copies – and one of them was stolen.

At the annual Northern Night fundraising auction an autographed copy of the weighty tome sold for a healthy £120, to a man in a comedy hat, decorated in scores of badges.

However, that was only half the sum paid out for dinner at the Commons with jovial Brownite backbencher Dave Anderson. The Blaydon MP looked rather pleased.