British forces must withdraw from Afghanistan as quickly as possible before any more troops are killed, Liberal Democrat former leader Lord Ashdown has said.
In a damning assessment of the campaign in Afghanistan, he said allied forces had failed to build a sustainable state and establish a government which was untainted by corruption.
Prime Minister David Cameron has said British forces will have been withdrawn from Afghanistan by the end of 2014 but writing in the Times, Lord Ashdown said it should be sooner.
He said: "We cannot pretend there is any more to do in Afghanistan. The urgent priority is to get out. It is not worth wasting one more life in Afghanistan. All that we can achieve has now been achieved. All that we might have achieved if we had done things differently, has been lost.
"The only rational policy now is to leave quickly, in good order and in the company of our allies. This is the only cause for which further lives should be risked."
Lord Ashdown said the failure to establish a functioning state was not the fault of British troops but of the international community to work with the country's leaders and neighbours.
He added: "The international community in Afghanistan needed to speak with a single voice in pursuit of a single plan with clear priorities. Instead we have been divided, cacophonous, chaotic. We should have concentrated on winning in Afghanistan where it mattered, instead of distracting ourselves with adventures in Iraq.
"We should have engaged Afghanistan's neighbours, instead of going out of our way to make them enemies. Our early military strategy should have been about protecting the people instead of wasting our time chasing the enemy.
"We should have made fighting corruption our first priority instead of becoming the tainted partners of a corrupt Government whose writ, along with ours, has progressively collapsed as that of the Taliban in the south has progressively widened."
His comments come amid an increasing number of green-on-blue attacks where members of the Afghan National Army have turned on allied troops. On Remembrance Sunday, Captain Walter Barrie was playing in a football match between British soldiers and members of the Afghan National Army at his base when he was shot at close range in the Nad-e Ali district of Helmand province.