Gordon Brown is under pressure to mark the fifth anniversary of the Iraq war next month by announcing an independent inquiry to ensure vital lessons are learnt.
Some allies have warned the Prime Minister that Labour will not win back disaffected supporters who deserted the party over the 2003 invasion unless he draws a line under the affair. They argue a public inquiry would enable him to bring "closure" to an episode which divided the nation.
Mr Brown has not ruled out an investigation but has hinted he would not want one while British troops remain in Iraq. Supporters of an investigation say that, now British forces have pulled back from a combat to an "overwatch" role in Basra, the time is right.
The Prime Minister is not persuaded that "looking back" at the build-up to war and the lack of preparations for its aftermath would be the right course of action. He may stall, arguing it would be better to "look forward" to Iraq's future.
In a letter to Mr Brown yesterday, the Labour-affiliated Fabian Society said there was a widespread recognition among people who held different views about the war of the need to learn lessons. It said a full inquiry would ensure a rounded assessment of the pre-war diplomacy, the intelligence failures over Iraq's weapons of mass destruction, the conduct of the conflict and the problems with post-war reconstruction.
The Fabians are Brown loyalists and their leadership includes Ed Balls, the Schools secretary, who is the Prime Minister's closest political ally. The Fabians believe an Iraq inquiry would help Mr Brown's drive to create what he has called a "new global society" by reforming international institutions after a new US president takes over next January.
Sunder Katwala, the Fabians' general secretary, told Mr Brown: "This agenda should be at the heart of the Labour Party's thinking as it creates a new progressive foreign policy agenda to put forward at the next general election." He warned the Prime Minister: "Our ability to pursue this debate within Britain and beyond and to engage people will depend on acknowledging and learning the lessons of Iraq, showing a clear commitment to building from these to create the new internationalist agenda we need for the future. A public inquiry into Iraq would be an important way to achieve this."
The Fabians pointed out that America was now taking stock of the intervention in Iraq during the presidential election. They said Britain should join the debate on how "stronger international co-operation can provide a more effective alternative."
Pressure on Mr Brown to call an inquiry is expected to grow as the anniversary approaches. The Tories and the Liberal Democrats have already called for an overarching investigation, arguing that the four carried out while Tony Blair was Prime Minister were piecemeal and that their terms of reference were restricted. These included Lord Hutton's inquiry into the death of the weapons expert David Kelly.
Labour MPs will also demand a fresh look. Peter Kilfoyle, the former defence minister, said a wide-ranging investigation would boost Mr Brown's prospects at the next general election. "It would be a significant factor," he said. "It would be a way of him showing a major difference between him and his predecessor."
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