The New Statesman editorial endorsing Ed Miliband for Labour leader described the decision to invade Iraq as "a great wrong, a moral failure". His brother's support for the war, it implied, was one of the reasons he does not qualify to be the change candidate that Labour and Britain needs. But the British voter is not an especially moral creature. If it was just a matter of right or wrong, however great, David Miliband might lose my vote as well as the NS's support, but he would certainly remain capable of winning an election.

What is summed up in the word "Iraq", however, remains a determining political issue. David's record on it will prevent him from winning a general election. I like David. I admire his energy and he seems to me to be more thorough, hard-working and professional than the other candidates, and to have a greater grasp of policy. These qualities have helped him gain a staggering range of endorsements across the UK media from the Financial Times to the Evening Standard, as the man they can do business with. But the legacy of the Iraq decision overshadows all this. It feeds into quite fundamental issues of trust and the role of the state. Labour will be forced to shape up on both issues to if it is to win back the decisive sectors of the electorate whose vote is not predetermined by party loyalty. David will be skewered.

First, trust. For Labour to win, its leader has to be able to give an honourable account of him or herself. The technical justification for the war was Saddam Hussein's possession of WMDs, weapons of mass destruction, and his refusal to surrender his alleged stockpiles despite UN resolutions requiring him to do so. David said at the NS hustings that if he'd known then that there were not, after all, WMDs in Iraq, he would not have supported the war. Or, to put it another way, that he originally supported it in good faith and let's move on. This positioning -- the decision was wrong but personally he was not -- is hardly honest, even on the narrowest of grounds.

No one who followed it believed that the war was fought because Saddam had WMDs. Tony Blair, as is well documented, had decided soon after 9/11 to support George W Bush, whatever he did. And, as Michael Elliott reported in Time magazine, in February 2002 Bush put his head around the door of a meeting at the White House where three US senators were being briefed by Condi Rice, and told them, "Fuck Saddam, I'm taking him out."

A year later, after Saddam had indeed been taken out, Paul Wolfowitz, one of the war's architects, told Vanity Fair that they settled on WMDs as the casus belli "for bureaucratic reasons". Yes, many intelligence experts thought Saddam had kept some rusting weapons. But no one believed they represented a danger to the west. The exaggeration was worse than contrived.

Take just one example, still unreported because it exposes the Blair regime's clinical disregard for truth: the British government stated in the executive summary of its September 2002 report, "As a result of intelligence we judge that Iraq has continued to produce chemical and biological agents". Blair sexes this up in his foreword: "What I believe the assessed intelligence has established beyond doubt is that Saddam has continued to produce chemical and biological weapons."

In fact, it was impossible for Saddam to have been producing new chemical agents, let alone chemical weapons, without this being observed by surveillance. The toxicity of the vapours demands massive ventilation for any level of manufacture, and this would have been identified. (See the openDemocracy interview with Ron Manley, who oversaw the destruction of Saddam's chemical armoury after 1991, but was never asked to share his expertise, though still attached to the Ministry of Defence.)

In other words, it is not just that Hans Blix, the head of the UN weapons inspection team, should have been given more time. The UK government was not interested in investigating the seriousness of the alleged "threat" of WMDs. They were a bogey that was itself contrived. Saddam was overthrown because the US knew he was weak, not because he was a danger. For someone in David's position to suggest even now, in public, that had they known there were no WMDs in Iraq the invasion would not have been justified, perpetuates an untruth, namely that the motive of ridding the world of Saddam's WMDs was genuine. The government misled the public about its reason for the war. By pretending otherwise, David continues to justify an appalling breach of confidence.

Room for redemption?

It remains an abuse of trust that angers the principled right, which draws on Britain's military folklore. The Daily Mail, the Telegraph and the Independent all supply readers with allegiance to this tradition and they are not going to allow Labour to forget it. Were he to become the party's head, David would be inescapably identified as an apologist and accomplice of the betrayal of Britain's military integrity.

We all make mistakes, especially in politics. People must be allowed to redeem themselves; otherwise, everyone gets trapped in sectarian shallowness. If David had said that the line on WMDs deceived him, he would at least have opened up a space between himself and the perpetrators of the concoction. More important, there was a decisive moment when he could have redeemed himself on Iraq.

On 12 November 2007, Gordon Brown made his first full-scale speech as prime minister setting out his approach to international affairs. He called for "hard-headed internationalism", opposed anti-Americanism and didn't mention Iraq. But as he went out of his way to regret that the international community had not taken action over the Rwanda genocide, the omission of the invasion of Mesopotamia was a clear signal that he wanted to distance himself from it. Typically, Brown did so while failing to be decisive.

The next day Brown's attempts at "renewal" were ambushed. His new foreign secretary was asked by the BBC whether the "same decision" on Iraq would still have been made under Brown's new direction. "Absolutely," David Miliband replied, and he insisted: "No one is resiling from the original decision."

Colin Brown's report in the Independent went on to say that Labour critics of the war were "disappointed". This is an understatement. At the time, David knew just as well as he does now that Saddam had no WMDs. But he didn't mention the fact as having any bearing; his support for the invasion was 100 per cent pure Blair and he locked his successor in to it.

Two points follow. First, a question: what has led David to change his mind between 2007 and 2010? Even his apparently low-key, technical positioning, that he would not have supported the invasion had he known there were no WMDs, is inconsistent and unsustainable. He backed it unconditionally well after he knew.

Second, he has a direct responsibility for the fact that Labour has not been able to put Iraq behind it. Earlier in the summer, he gave an eloquent Keir Hardie lecture. Looking back over the immediate past he said, "I agreed completely with Gordon Brown, when he became prime minister in 2007, that we needed renewal. I supported and voted for him. I agreed that we needed greater moral seriousness and less indifference to the excesses of a celebrity-drenched culture . . . But, it didn't happen."

One of the reasons it didn't happen is that David Miliband helped to prevent it from happening. He supported the previous celebrity prime minister when Brown sought change. In 2003 he was only a junior member of the team. By 2007, as foreign secretary, he shared responsibility for Labour failing to renew itself by backing the Iraq decision 100 per cent.

Talk versus walk

Jon Cruddas, who voted for the war, like so many of David's supporters, says the Keir Hardie address was one of the factors that persuaded him to endorse David. When James Purnell resigned from the cabinet in 2009 because Brown was sure to lead Labour to defeat, Cruddas gave a speech to a Compass conference. He ridiculed the arguments of the Purnell faction, who said they agreed entirely with Brown's policy but not his leadership. They were, literally, he mocked, "rebels . . . without a cause"!

It was a brilliantly funny rebuke. But was Cruddas demanding that they embrace different policies or was he telling them not to take a stand? For while Cruddas sets out his cause, where is the rebellion? From Iraq to 42 days' internment without trial, when push comes to politics, Cruddas, like David, has the rhetoric but not the will to strike.

Below the Plimsoll line of acting honestly, there is the great bulk of public opinion. Historically, Iraq was a unique war in terms of popular support. With appeasement in 1938, Prime Minister Chamberlain had most of the public behind him, even though he was wrong. When Winston Churchill was defiant and far-sighted in 1940, he had wide public and cross-party backing. When Anthony Eden launched the Suez expedition (also dishonestly), the assault on Egypt was popular, even though the strategy was disastrous. Over the Falklands, Margaret Thatcher had public opinion on her side, whatever you thought about fighting in the South Atlantic. Throughout the cold war, the British overwhelmingly backed deterrence. But with Iraq, for the first time, the government committed the country to a major conflict while millions marched against it despite the leadership of both main parties and most of the press.

Britain's informal constitution has at least two abiding rules -- unwritten, of course -- that have ensured its longevity. The first is to ensure broadly speaking popular consent for the regime and its wars. Consent can be highly manipulated and is different from democracy. Arguably, certainly from the point of view of a political elite, it is better to have consent without democracy than democracy but not consent. In the case of Iraq, Britain had neither.

That was bad enough. But the second informal understanding of the British regime is that while the public is foolishly conservative or dangerously populist and generally grasping, short-sighted but foolishly in love with conventional forms of power, the elite are wiser, more far-sighted and know what is best. It is the validity of this presumption that allows the country's rulers to retain consent over the long run.

With Iraq, this state of affairs was turned upside down. The real, unspoken reason for the Chilcot inquiry is to work out what do to re-establish the credibility of a military, administrative and intelligence establishment that got it completely wrong.

How wrong, and it is good to be reminded, was summed up before the war by an obscure Democratic politician in Chicago who, despite his ambition, broke ranks with his party and, in effect, spoke for millions in his own and our country when he said about Saddam Hussein:

He is a brutal man. A ruthless man. A man who butchers his own people to secure his own power. He has repeatedly defied UN resolutions, thwarted UN inspection teams, developed chemical and biological weapons, and coveted nuclear capacity. He's a bad guy. The world, and the Iraqi people, would be better off without him.

But I also know that Saddam poses no imminent and direct threat to the United States, or to his neighbours, that the Iraqi economy is in a shambles, that the Iraqi military a fraction of its former strength, and that in concert with the international community he can be contained until, in the way of all petty dictators, he falls away into the dustbin of history. I know that even a successful war against Iraq will require a US occupation of undetermined length, at undetermined cost, with undetermined consequences. I know that an invasion of Iraq without a clear rationale and without strong international support will only fan the flames of the Middle East, and encourage the worst, rather than best, impulses of the Arab world, and strengthen the recruitment arm of al-Qaeda. I am not opposed to all wars. I'm opposed to dumb wars.

David Miliband went along with the Blair view that the millions who thought this didn't "get it" when we took to the streets on 15 February to protest against the coming invasion. In fact, the millions were wise and he was dumb.

General crisis

What David needs to explain, therefore, is not just why he was wrong, but why we the public got it right. The issue is not only about him and his judgement, but his explanation, as the would-be leader of a democratic Britain, of why, when the public was right, we were ignored. The public being not just Labour supporters but also the hated Lib Dems, patriotic Conservatives, Greens, Scottish Nationalists, Robin Cook, Diane Abbott and, indeed, Uncle Tom Cobly as well as President Chirac, Chancellor Schröder, Joschka Fischer, Barack Obama (they were his words in Chicago) and all. How come we knew what was going on when he didn't? It is the answer to this question that tells us what kind of power (and there are different kinds) he feels he has to represent.

David is now saying that Labour has to be a "movement" and he is funding a thousand citizen campaigners to help achieve this. But Labour was rarely, if ever, more of a movement than in February 2003. Even a majority of Labour MPs not on the government payroll voted against the war, which was only endorsed by the House of Commons thanks to the Tories. Yes, indeed, a party of the left needs also to be a movement. But a movement has to embody judgements; it has to stand for something. When Labour was last a movement David opposed it. Why does he think that the movement called it right -- and six years later what remained of it then got 42 days right, while he didn't? Perhaps Jon Cruddas can explain.

The question goes to the heart of current British politics. For perhaps the first time since the franchise was cleaned up in 1832, the voting public feels that the political elite do not represent the country. The public has always been justifiably cynical in thinking its leaders support the class system, but at least it was our class system! In the case of Iraq, the elite acted in the interests of Washington and George Bush. They told us that we had to back globalisation for our own good. When the crash came, it turned out that they were representing the bankers, not the British. Then the expenses crisis broke, and the catastrophic decline in trust that followed was less about what some MPs took for themselves than what MPs as a whole permitted.

At first, the freshness and surprise of the coalition made it seem that it would be able to distance itself from this general political crisis. It may find it increasingly hard to sustain this, and it is certainly the case that unlike "sleaze" and John Major's government, the corruption of the Noughties is cross-party.

But it does not follow that Labour is not specifically identified with the abuses of power that marked this century's opening decade. It expanded the powers of the state far too much, threatened our liberties and deployed its powers on behalf of vested interests, especially international financial ones. The public knew this, has not forgotten and anyway will be reminded of it. In these circumstances, to dismiss the Iraq decision as "the past", as David Miliband does, when it opened the gates, and to belittle the issue of trust that it symbolises, is a strategic failure of political judgement. In whose name does he want Labour to rule the UK? Because of its reckless statism, from ID cards through subsidising bankers to the Budget deficit, and above all its military adventurism on behalf of the United States, this will be a major front in the coming battle for Labour to re-establish its claim to govern.

Milisisters

The new generation bidding to lead Labour are not interested in having the kind of bunfights that permit the press to destroy them. Inheritors of 13 years in office, they know what it takes to win; the disciplines of ruling come naturally to them (including Diane Abbott). Today, the question is what to do with power once in office and how to build support for any reforms they carry out. Something that Mandelson, Campbell, Brown, Blair et al, for all their skill at "persuasion", were incapable of achieving. Boring as the leadership contest may be to outsiders, this is the underlying seriousness of it.

Delivery, it seems, will not come from internal ideological correctness. Perhaps this is why partnerships seem to go down well in British public life. What are David Cameron and Nick Clegg but a replacement for Blair and Brown? Voters find ideological disputes between party factions weird. They make them feel excluded, and the media hammers "splits". But who isn't familiar with strong personal differences between individuals tied together in a relationship?

In an era when the spectacle demands personalisation yet dislikes the cult of the individual, partnerships, with their human tensions and difficulties, may be inherently attractive. The Blair-Brown diarchy in Downing Street has been replaced by another, and in a similar way the coupledom of the Milibands is an attraction. They are the Williams sisters of Labour Party politics, outsiders delivering a new style and professionalism to the game. Is David the Venus who may win first and Ed the Serena who shows greater determination when pushed to prove himself?

If they can continue to play together while playing each other, Labour could have a winning team. But it is as certain as things ever are in politics that, however much David is an asset in the larger game, he will be an election-loser if he is appointed captain.

Anthony Barnett is co-founder of openDemocracy and co-edits its British blog, OurKingdom.