Defeated but by no means disgraced in this month’s election, Britain’s Labour Party is now engaged in the search for a new leader. In contrast to the rapid coups and counter-coups that we are used to in Australia, this is a drawn-out process that will conclude with a ballot in August-September, weighted one-third each MPs, unions and party members.

With British politics poised at a very interesting point, the future will depend a great deal on how well Labour can get its act together, so it’s clearly worth taking the time to get things right. One can only speculate on how different things might have been if our Liberal Party had gone through a similarly careful process after its 2007 defeat, instead of holding three successive panicky leadership elections, all decided by tiny margins.

Labour’s acknowledged frontrunner is David Miliband, former foreign secretary and loyal supporter of Tony Blair, who repeatedly turned down suggestions to run against Gordon Brown in 2007, or to subsequently challenge him. Most of his likely opponents (nominations close on 9 June, and candidates need the support of 33 MPs to run) are also intimately connected with Blair’s legacy — the Labour front bench is a pretty homogeneous place — but the top priority of the anti-Blair vote will be to stop David Miliband.

Hence the great interest in the view offered on Friday by one of those rivals — David’s brother, Ed Miliband — that the party needs to come to terms with the Iraq war, which had led to “a catastrophic loss of trust in Labour”.

Ed Miliband was not in parliament in 2003, but he says that even at the time he thought it was a mistake. Ed Balls, another leadership contender, admits supporting the war but now describes it as “an error for which we as a country paid a heavy price”. David Miliband, on the contrary, argues that the party should put the controversy behind it and that “it was time to move on.”

My view (which may not surprise regular readers) is that the Iraq invasion was so far outside the bounds of civilised conduct that it has poisoned the well of politics across much of the democratic world, and that no-one who fails to understand that can be a credible leadership contender. John Kerry and Hillary Clinton are perhaps the most obvious examples of falling foul of this rule.

But even those who disagree with my position can hardly escape the realisation that it has been a deeply divisive issue within the Labour Party. It is the thing that most defines Blair’s leadership, and drove the undermining of him by many MPs who had no great love for Gordon Brown.

David Miliband probably feels that, whatever his private feelings about Iraq, he will always be seen as the most Blairite candidate; since it is too late for any credible revisionism on his part, he can only hope that the whole issue will go away.

But it is disturbingly common for politicians to think that a call to “move on” is an acceptable substitute for an apology or an admission of error. Recall John Howard’s deathbed conversion to the need to address climate change, which was unaccompanied by any acknowledgement of having been wrong, or even of having changed his mind.

Until those who were complicit in the Iraq adventure face up to the enormity of what they did, it will remain a real and divisive issue.