It is therefore vital to the UK that Afghanistan becomes a stable and secure state that is able to suppress violent extremism within its borders.
In a speech on October 14 October 2009 about the UK military presence in Afghanistan, Prime Minister Gordon Brown said:
"Our objective is clear and focused; to prevent al Qaeda launching attacks on our streets and threatening legitimate government in Afghanistan and Pakistan.
"But if we limit ourselves simply to targeting al Qaeda — without building the capacity of Afghanistan and Pakistan to deal with terrorism and violent extremism, the security gains will not endure."
British Forces are operating in Afghanistan because it became a source of terrorism that threatened Britain and the rest of the world.
The Taliban gave safe haven to Al Qaeda, which allowed terrorists to plan and carry out terrorist attacks around the world, including the atrocities of 11 September 2001.
That is why the UN authorised a NATO-led military intervention.
It is under NATO's International Security Assistance Force that the British Armed Forces, along with the militaries of over 40 other nations, are deployed to Afghanistan.
Working as part of this international community, the UK is supporting the Afghan government as it builds a peaceful and resilient nation, shaped by the will of the Afghan people.
Right now British Forces are taking the fight to the Taliban in southern Afghanistan, facing down the insurgency, protecting the Afghan people and laying the conditions that will contribute to stabilisation efforts.
They are also providing direct military support to the Afghan National Security Forces including the Army and Police through training and mentoring, building up those institutions so they can take on the job of confronting the insurgency themselves.
Twenty years of war completely destroyed Afghanistan's infrastructure, economy and institutions.
UK forces are therefore also working alongside civilians in multi-national Provincial Reconstruction Teams to help the Afghan State increase in size and capacity so that it can protect its people, giving them physical and economic security.
The military intervention in Afghanistan is just one aspect of the UK's involvement in supporting the country.
The UK is working relentlessly on all fronts to help the Afghan Government improve governance, both nationally and locally, tackle corruption and the drugs trade, build up the rule of law, promote economic development - investing in infrastructure, legal alternatives to poppy, jobs - and improve access to education and healthcare.
The UK remains committed to these things. We are not imposing a Western model, but are working alongside 60 countries to give the people of Afghanistan a stake in their future.
It is a hard job. Progress is slow, but the progress we have made is real, and we are working towards the day when foreign troops are no longer needed on the frontline and Afghanistan can stand up to terrorism itself and offer its people hope for the future.
Gordon Brown said in his 14 October 2009 speech:
"We will have prevailed in Afghanistan when our troops are coming home because the Afghans have not only the will to fight but the ability to take control of their own affairs."
Walking away now would not solve the problem but compound it. It would risk recreating the chaos in which terrorism could re-establish itself.
Failure would deal a serious blow to the credibility of the UK, NATO and the international system, would hand victory to violent extremism with all that would entail, and would damage regional stability.