The war in Afghanistan is not worth one more life and Britain should withdraw immediately, Lord Ashdown has said.
Writing in The Times on Friday, the former Lib Dem leader said it was "crystal clear" that the West had lost the war and that "the only rational policy now is to leave quickly".
"It is not worth wasting one more life in Afghanistan. All that we can achieve has now been achieved," he said.
"The only outcome of staying longer is more deaths for no purpose; most of them now caused not by the enemy in front of our troops, but by the enemy among them."
Since 2001, some 438 British lives have been lost in Afghanistan and this year alone 14 have been killed by members of the Afghan army or police force.
Ashdown said that the Armed Forces emerge from the war "untarnished" as they had beaten the Taliban in almost every battle. But he said the failure had been not military, but political.
"We should have understood that victories on the battlefield are meaningless if you can’t translate them into political progress and better lives for ordinary people," he said.
Ashdown, who served in the Royal Marines and SBS special-forces before entering politics said it was time to "abandon the pretence that there is more of substance to be achieved in Afghanistan".
"The main thing to do now is leave as quick as we decently can, providing as much protection for our friends as we can, in the best order that we can and with as much of our equipment as we can," he said.
David Cameron has pledged to withdraw all combat troops from Afghanistan by 2014. On Thursday the US began negotiations with the Afghan government over the level of troop presence that would remain after that date.
In 2009 Ashdown argued against pulling out, telling the House of Lords at the time that while failure was "quite close" leaving "would have baleful consequences including abandoning the clear majority of Afghans who want us to be there".
However in his Times article today the former Lib Dem leader said Britain and its allies should have "grabbed the best opportunity for a negotiated peace three years ago" instead of "continuing our blind pursuit of the illusion of outright military victory".