Sir Christopher Meyer acknowledged that leaving Iraq would be "painful", but said the mission was not worth the death of one more serviceman. "I personally believe that the presence of American and British and coalition forces is making things worse, not only inside Iraq but the wider region around Iraq. The arguments against staying for any greater length of time themselves strengthen with every day that passes," Sir Christopher said.
He added: "I think the Iraqis are in fact sorting themselves out - often bloodily - independent of what we're doing."
The former diplomat, posted in Washington in the runup to the 2003 invasion, was giving evidence to the Iraq Commission in London. The cross-party group - modelled on America's Iraq Study Group - was set up by the Foreign Policy Centre thinktank and Channel 4 to examine possible options for Britain's future role.
British commanders in Iraq have drawn up a plan for the withdrawal of almost all UK troops within 12 months, as one of several options to be presented to Gordon Brown when he takes over as prime minister. But Sir Christopher said Mr Brown was unlikely to announce a unilateral troop withdrawal that was not coordinated with the United States.
He acknowledged that foreign policy decisions were always "fraught with risk". But asked about criticisms of withdrawal, he replied: "It always seemed to me this was one of the key moral arguments in Iraq, that however bad things were ... the overriding requirement for us was to be able to say to parents and relatives in Britain, your sons and daughters did not die in vain. I think we have now crossed the line - we now have to say the mission is no longer worth another life of a British or American serviceman."
Sir Christopher's controversial book, DC Confidential, argued that the coalition failed to plan for securing and rebuilding Iraq in the aftermath of the invasion.
Sir Richard Dannatt, head of the army, said last year that the British should "get ourselves out sometime soon because our presence exacerbates the security problems".
Oliver Burch, of Christian Aid, told the commission that reconstruction efforts by the military had made the work of aid agencies harder in some ways.
It meant military operations were run alongside humanitarian work.
"For that reason those who do not like the coalition forces do not like NGOs either," he said.
The commission, chaired by Lord King, Lord Ashdown, and Lady Jay will report in mid-July after hearing evidence from a range of military and policy experts.
© 2007 The Guardian