General Sir Michael Rose, who commanded the United Nations Protection Force in Bosnia-Hercegovina from 1994 to 1995, said coalition forces in Iraq were facing an impossible situation."
"There is no way we are going to win the war and (we should) withdraw and accept defeat because we are going to lose on a more important level if we don't," he said.
Though the coalition could not simply "cut and run," Rose said announcing a withdrawal date would help to dampen down the violence between Sunni, Shia and Kurdish factions.
"Give them a date and it is amazing how people and political parties will stop fighting each other and start working towards a peaceful transfer of power," he said.
Rose was speaking at the annual Hay Festival of Literature and the Arts in Hay-on-Wye, on the Welsh border with England.
The retired general who has written a book on the American War of Independence, made comparisons with the 1775-1783 conflict between Britain and the Thirteen Colonies.
He said: "How was it a small and extremely determined body of insurgents, thieves and deserters could inflict such a strategic and potentially disastrous defeat on the most powerful nation in the world? "The answer will be familiar to anybody who is looking at what is happening in Iraq today. "Those who don't read history are condemned to repeat the mistakes of the past." He said the allies in Iraq should have deployed more troops and not used a conventional war strategy.
"You don't win wars by regime change but by changing attitudes," he said.
He said that Iraq should have been low on the priority list compared tHe said that Iraq should have been low on the priority list compared to Afghanistan, conflicts in Africa and the battle against international terrorists."