The purpose of the Nato mission in Afghanistan is clear. It is to ensure that Afghanistan does not become a safe haven for international terrorism that would endanger our national security and that of our friends and allies. Our long-term strategy is also clear; it is to give the emerging Afghan democracy the means to do this job for itself.

Afghan security forces are not yet strong enough to discharge this role. That is why Nato forces are seeking to deny freedom of manoeuvre and territory to the Taliban and their al-Qa'ida allies.

The strategy is absolutely the right one. It does not rely exclusively on military means. But it does require sufficient military resources to be effective. First, we need enough resources to help accelerate the training of local security forces. Second, we need enough troops now to hold and secure the ground, so that the Afghan Government and the UN Mission can deliver economic and social re-construction. Without security there can be no re-development. Without security we can never create the right conditions for eventual political reconciliation between those elements of the insurgency who might be willing to renounce violence and the Afghan Government.

Critically, our strategy does require a credible and capable partner in the shape of the Afghan government itself. This requires further work. The strategy also requires further military re-enforcement – this is clear from the McChrystal report.

There is no credible alternative strategy. Pulling out would not make the threat from terrorism go away – but magnify it. Our losses are grievous, but they would be even higher if we were to falter now.

John Hutton was Defence Secretary from October 2008 to June 2009