What did you do in the Iraq War, Gordon?

One of the many myths about the road to war against Iraq in 2003 was that Britain was powerless to alter the course of history. Had we not joined our Atlantic ally, the argument runs, the US would have gone it alone anyway. Such a view masks the fact that it is plausible to argue that choices made by Tony Blair and by Gordon Brown could have delayed or prevented the war.

Much has been written about Mr Blair's decision-making. What has not been the subject of intense scrutiny is the direct and indirect responsibility other political leaders bear. The Conservative Party was one such actor that failed to stop Mr Blair. Public opinion could have exerted more pressure and, most significantly of all, key members of the Cabinet - including the current Prime Minister - could have averted the disaster.

What if Iain Duncan Smith, who was then leader of the Conservatives, had taken an anti-war position and whipped his MPs to vote accordingly? Such a significant flip might appear to lack credibility until we remember that one of the strongest anti-war voices on the opposition benches was Kenneth Clarke, who was defeated for the leadership by Duncan Smith in 2001.

Public opinion was against a unilateralist US-led intervention, but it was not against war per se. Polls show that the public preferred a UN-backed operation; once this was off the table, there was a swing in favour of military action. Had the British people opposed war irrespective of the mood of the UN Security Council, then the pressures on MPs to vote against the Government on 18 March 2003 would have been much greater.

It is also correct to believe that key members of Mr Blair's Cabinet had the power to slow, perhaps even halt, Britain's rush to war. We know that Robin Cook resigned as Leader of the Commons immediately before shock and awe was unleashed on Iraq: had other heavyweights joined him, the impact would have rocked the Government.

There is no doubting the power of Mr Cook's stance on Iraq: he had received all the intelligence briefings and worked out that Saddam Hussein had no usable weapons of mass destruction. Moreover, he was honest enough to realise that the commitment to a rule-governed international order could not be squared with unilateral action that lacked both procedural and substantive legitimacy.

The day of reckoning in the Cabinet was the meeting on 17 March 2003 when Lord Goldsmith set out his revised opinion on the legality of military action. What if Mr Brown had threatened to resign, stating that he had concerns about the evidence against Iraq and had doubts about the legality of the war in light of the failure to get a second UN resolution? News of a divided Cabinet would have provoked more than 139 Labour MPs to vote against, and possibly stirred the Tories to oppose the Government. At this point, Mr Blair's choice would have been to call back the UK deployment or to resign as Prime Minister.

Such a catastrophic blow to the Anglo-American alliance, coupled with Turkey's decision not to allow US forces to attack Iraq from Turkish bases, would most likely have delayed the war. Given more time, Hans Blix's UN inspectors would have come to the view that, contra Donald Rumsfeld, an absence of evidence was indeed evidence of absence. It is not inconceivable that, faced with a massive consensus against forcible action, even the neoconservatives might have blinked.

We know that Mr Brown admires courage greatly. What we do not know is why he did not follow the courageous example set by Mr Cook. Diaries and memoirs record how, at the Cabinet meeting of 17 March, Mr Brown robustly defended Mr Blair's strategy. Before then, he had been virtually silent on the issue. Opponents put Mr Brown's silence down to the fact that he feared the impact that losing a vote in the Commons would have had on the Government overall, particularly his own position as the natural successor.

Mr Brown may have believed that a U-turn by Britain at the eleventh hour was not going to alter the Bush Administration's decision, while incurring significant costs in terms of the Anglo-American alliance. This was a misjudgment. It does not appear that "old Europe" has paid a high price for opposing the war. Worse still, Britain's claim to be a force for good in the world has been fatally undermined.

There have been countless articles and documentaries about Tony Blair's justification for sending our armed forces to fight in Iraq. His beliefs have been questioned, his psyche scrutinised, his judgment criticised. Contrast this with the absence of scrutiny given to Mr Brown's role. On every other major issue during the "TB" years, we know what "GB" believed. It is curious that this is not the case about his thinking on Iraq at the moment of decision.