“You voted for it, why are you clapping?” David Miliband’s question, overheard at the Labour conference on Tuesday, lies at the heart of the brutal struggle for the party leadership which had just seen him beaten by his own brother Ed, a result which plainly surprised the winner as much as it shocked the loser. His words sum up the dilemma which haunts Labour, the shadow they can’t escape from.

After Labour had won three general elections under his leadership, Tony Blair finally departed in the summer of 2007, possibly to bring peace to the Middle East, certainly to accumulate a large personal fortune. He was succeeded as prime minister by Gordon Brown, who for the best part of ten years had been waiting to take over, with ever-increasing anger and bitterness. When he he won his crown at last, it soon crumbled, and when the financial crash came in late 2008, his authority collapsed as well.

He hung on until the bitter end and, after the general election in May gave no party an absolute parliamentary majority, he tried to hang on even further at Downing Street. Then, before he resigned the prime ministership, he announced that he would be resigning as Labour leader, and so put in train the lengthy and in some ways bizarre process of choosing a new party leader.

For 75 years after the Labour Representation Committee was renamed the Labour Party in 1906, the party chose its leaders by a simple election among its Members of Parliament. Then 30 years ago came the attempted takeover of the party by the extreme Left. It failed, but the conspirators did impose a new—and wholly absurd—system for electing leaders, the “electoral college,” although one veteran MP said that time that it sounded more like an electoral kindergarten There are three distinct “electorates”: Labour MPs and members of the European parliament; party members; and the unions, traditionally the “industrial wing” of a Labour movement whose political wing was the Party. More to the point, the unions provided the party with its funds.

Not even the electoral systems of the Venetian Republic were more abstruse, nor their outcomes so difficult to forecast, partly because the different electorates are so decayed. In the middle of the last century, genuine individual membership of the Labour Party—as oppose to the millions of members nominally “affiliated “ through their unions—nearly touched a million. It fell steadily for decades, until a “Blair bounce” sent it up to 405,000 in 1997, but the long hangover which followed the high saw it fall back to below 180,000, nearly the lowest level since the Party was founded. Union membership has also fallen steeply. The unions are meant to ballot their members by some means over the party leadership, but this appears to have been another legal fiction. And so a few union bosses meeting in private tipped the balance in favour of Ed.

To all of that was added the Wagnerian drama of a fratricidal contest. Five candidates were nominated for the leadership, but it soon became clear that the only two seriously in the running were the brothers, David and Ed Miliband. There had been a prevailing assumption (for what such assumptions are worth) that David would be the obvious successor as leader, and for most of the past four months he has been easy favorite with both commentators and bookmakers. He was, besides, Tony Blair’s anointed heir—but then that may have been decisive in another way.

Much has been written about the brothers’ background. Their father Ralph Miliband was Polish Jewish by origin, and was living in Belgium as an adolescent when he war began, before he escaped on the last boat to England in 1940. He managed to go to the London School of Economics, and then joined the Royal Navy, before becoming a celebrated Marxist writer and teacher, and a great oracle of the New Left. "I think there is an anti-Semitic trend, however weak, in every non-Jew," the young Ralph wrote, but he was what Isaac Deutscher—another old left revenant who became a hero to the New Left—would have called “non-Jewish Jew,” one of a long line from Marx himself onwards who discarded traditional faith for the new religion of revolutionary politics.

The Miliband brothers had no religious upbringing of any kind, and have no interest in Zionism. But nor do they have any in Marxism, which they discarded in turn for everyday practical politics, and plain ambition, as they became a pair of apparatchiks. David was still in his twenties, fresh from Oxford and MIT, when he became head of Blair’s “policy unit” before the 1997 election. He entered Parliament in 2001, was made a junior minister almost immediately, then entered the Cabinet, and was Foreign Secretary at 41; he is now 45.

His 40-year-old brother also had a precocious career. A youthful advisor to Gordon Brown even before Brown became Blair’s Chancellor of the Exchequer, he became an MP in 2005 and a Cabinet minister two years later. The two were therefore on either side during the soap opera or grand guignol known as “TB/GB,” the ferocious rivalry between Blair and Brown which poisoned and finally paralysed the last government. And that helps explain Ed’s victory on Saturday.

There are several salient facts about this leadership election. It was a photo-finish, with Ed winning, on the arcane calculations of the kindergarten supervisors, by little more than a percentage point. Then, the unions swung it for Ed, which means that he begins as leader in the public knowledge that a majority of his own MPs would have preferred someone else. But most significant of all was what Ed said in his acceptance speech.

For two days after the result was declared there had been a cloying display of fraternal affection, with David saying how proud he was of Ed and Ed saying how much he loved David. In truth, David is unmistakably very bitter. If his younger brother loved him so much, why did he engage in this public act of fratricide?

“Don’t worry about me. I’ll be all fine,” David said after he lost, biting his lip hard, and not quite adding a Nixonian, “You won’t have David Miliband to kick around any more,” before announcing yesterday his withdrawal from the Labour front bench, ostensibly to leave "an open field" to Ed and to forestall attempts by the media to inflame rivalry between their two camps.

But Ed’s acceptance speech, which required no advanced cryptanalysts to interpret it as a repudiation of the Blair inheritance, and above all the Iraq war, did more than enough to fan fraternal anger. Hence that electrifying moment in the conference hall. Iraq was ”an issue that divided our party and our country,” the new leader said, in a statement of the obvious unusual even by politicians’ standards.

“I criticise nobody faced with making the toughest of decisions and I honour our troops who fought and died there. But I do believe that we were wrong. Wrong to take Britain to war and we need to be honest about that.”

At that moment, David sat stony-faced with his arms folded, until he noticed that Harriet Harman, at present Deputy Leader of the Labour Party, who was sitting on his left, was vigourously applauding. Like David, she served as Cabinet minister under Blair. And at the time of the invasion of Iraq she not only voted for the war, she was Solicitor General, the sidekick of the Attorney General, Peter Goldsmith.

That is a grave matter: it has now been established beyond doubt—see the recent essay by the eminent English jurist Philippe Sands in the New York Review of Books—that in the spring of 2003, Goldsmith altered his opinion under pressure, declaring an invasion legitimate under international law when he had said shortly beforehand that an invasion would be of, at best, dubious legality. What did Harman know of that, we wonder?

And so, as David turned to the lady applauding on his left, the lip-readers and long-range mikes heard him ask her, “You voted for it, why are you clapping?” to which she inanely answered, “I’m clapping because as you know I’m supporting him.” So she is, just as she had supported Blair, and his war, and as most of her colleagues in the government did, and most Labour MPs.

How they now wish they hadn’t. How they wish Iraq has never happened. How they wish they could forget about Blair and his legacy. How hard that will prove.