He condemned Gordon Brown’s speech defending the campaign yesterday as lacking in “passion and charisma” and said the Prime Minister had failed to clarify confusion over the UK’s objectives in the country.

Lord Ashdown, who served as UN High Representative for Bosnia and Herzegovina until 2006, was put forward as the international community’s envoy in Afghanistan in 2008 but was blocked by the Afghan government.

He told Radio 4’s Today programme: “We have made catastrophic errors.”

“Events are still moving against us in Afghanistan and we have lost a great amount of time in turning things around.”

He said that the UK should not be asking whether our forces should be fighting the war instead, he said: “We should be asking ourselves a much more brutal question.

“Can we win it from where we are now?”

But he added: “It is too early to do that now, I want to see the results of these elections first.”

He said that it would be unhelpful if the international community passed judgment on the polls before Afghan authorities had completed their investigations.

The former Liberal Democrat leader also criticised Mr Brown’s leadership on the issue.

“In order to give the country a sense of why we are there we need a little more passion and charisma.”

Yesterday Mr Brown insisted the objectives in Afghanistan were “clear and justified” in a keynote speech the day after the shock resignation of Labour MP Eric Joyce.

Mr Brown told his audience: “Each time I have to ask myself if we are doing the right thing by being in Afghanistan.

“Each time I have to ask myself if we can justify sending our young men and women to fight for this cause. And my answer has always been yes.

“For when the security of our country is at stake, we cannot walk away.”

He also paved the way for an earlier-than-expected withdrawal of British troops from Afghanistan as he called for training of Afghan forces to be speeded up.

The Prime Minister proposed bringing forward a key Nato target to expand the Afghan army to 134,000 troops from 2011 to next year, which would require increasing the rate of training from 2,000 to 4,000 new troops per month.

On Thursday Mr Joyce, a former soldier and aide to the Defence Secretary, resigned saying: “I do not think the public will accept for much longer that our losses can be justified by simply referring to the risk of greater terrorism on our streets.”