Liam Fox: Why the Conservatives say we must stay on in Afghanistan

It has not been an easy week for British troops in Afghanistan. Two soldiers were killed by improvised explosive devices, which cause more than 80 per cent of our fatalities in Afghanistan. Five more were killed when an Afghan policeman opened fire on his British mentors.

Gordon Brown's speech on Friday was supposed to provide clarity to our mission in Afghanistan, but has done the opposite. On the one hand, we are told that our presence in Afghanistan is vital for our security and safety at home. On the other, we are told that we will not "put the lives of British men and women in harm's way for a government that does not stand up against corruption". If our mission in Afghanistan is a national security imperative, it cannot be conditional on the behaviour of others. Our troops are not fighting and dying in Afghanistan for Karzai's Government, nor should they ever be. Gordon Brown needs to understand this. Our troops are there for our security at home. Yesterday's attempt at clarification makes a bad situation worse if the Prime Minister was seriously suggesting that, with our troops involved in a vital international mission there, he will no longer recognise the government of Afghanistan.

However, this isn't to say that tackling corruption and establishing good governance isn't important. However, we need to recognise that Afghan governance is likely to look very different from governance as we know it in the West. Eighty per cent of Afghanistan's population lives in rural areas where Kabul's writ is largely nonexistent. Consequently, the main focus of improving governance should be directed at the provincial, district and village levels, at the level that can directly impact on the needs of the population. We must take a bottom up approach.

Let us make no mistake: we are engaged in a crucial struggle in Afghanistan. It is a national security imperative. A comprehensive strategy for Afghanistan must include clear, tightly-drawn, realistic objectives that are regularly reviewed; more rapid development of the Afghan security forces; and ensuring that the gains won by British forces on the battlefield are swiftly followed by reconstruction.

A month ago Gordon Brown said that 500 additional troops may be sent to Afghanistan based on "clear military advice from our chiefs of staff and our commanders on the ground on implementing our strategy and reducing the risk to our forces". To have 500 troops which are trained, equipped, and ready to go simply sitting in a barracks when the Prime Minister said our troops would get what they need to do the job sends a confusing message and shows indecision. Even if Gordon Brown approved the deployment of these troops tomorrow, it would still take weeks to get them to the frontline.

The same people who are calling for the withdrawal of international forces from Afghanistan are usually the same people who have criticised the West for neglecting Afghanistan after the fall of the Soviet Union. This, of course, led to the rise of the Taliban, the sanctuary of al-Qa'ida, and the attacks of 9/11. Leaving Afghanistan then was the root of our problems today. Leaving Afghanistan today will be the source of our problems tomorrow.

There are no cost-free options. Premature withdrawal will be seen as a victory for every jihadist around the globe and will have profound implications for our national security and the cohesion of Nato, which is why I think The Independent on Sunday is sadly mistaken.

This is not the time to go wobbly in Whitehall. We need leadership, a vision, and decisiveness that only a new Conservative government under David Cameron can provide.