Christina Lamb is an excellent journalist. When she comes to fear that our work in Afghanistan is Mission Impossible (News Review, last week), it is important to take note. Like her, I have flown with our troops across barren Afghan terrain, seen the difficulty of coordinating the international effort, heard from Afghans their frustrations with government corruption. But it is also important that we do not leap to the wrong conclusion. Her article describes setbacks and successes. I recognise many of the points she makes. So what should we learn? My answer is that we should learn from mistakes, build upon successes and use the coming winter lull in fighting to plan the next phase of the campaign.

Military “victory” in Afghanistan never involved killing all the Taliban or building British suburbia – democratic and genteel– in the Panjshir Valley. If either of these were our aims, we would indeed be on an impossible mission. But our true mission, consistently advocated by the UK government and our allies, has been to use military power to create the space within which Afghan institutions can become strong enough to resist the Taliban. That mission is certainly not impossible.

As General David McKiernan, commander of Nato and US forces in Afghanistan, said last week: “It is true that in many places of this country we don’t have an acceptable level of security. We don’t have good governance. We don’t have socioeconomic progress. We don’t have progress as evenly or as fast as many of us would like, but we are not losing Afghanistan.”

As Lamb says, the Taliban cannot defeat Afghan and coalition forces militarily. In 2008 the insurgency became further concentrated. Some 74% of incidents occurred in just 10% of Afghanistan’s districts, home to only 6% of the population. Nor is Kabul encircled. The Taliban lack the capacity to hold ground. In addition, while much of the insecurity stems from insurgency, some comes from growing criminality, including the drugs trade. Nato defence ministers have just given permission for their forces to do more to support the Afghan security forces in targetingdrug facilities. This year 18 provinces were poppy-free, up from 13 last year and six in 2006. Progress. Not enough, but progress all the same.

The military aspect of our task requires strengthening the Afghan army from its current level of 65,000 to 134,000 by 2012. A well-trained Afghan army on this scale will be able to provide its own framework of security. At present the Afghan army is able to lead just over half of military operations. McKiernan has called for additional troops and there are indications from across the US political spectrum that these may be forthcoming.

This military endeavour is not an indication that we or coalition allies or the Afghans are obsessed with a military “solution”. As Gordon Brown made clear to the Commons last December, we will support the Afghan government in drawing into the constitutional fold all of those – including former Taliban – who are willing to play by the constitutional rules. That is a political approach.

I have never needed persuading that our goals in Afghanistan also require skilful and determined economic, social and political engagement. Those delivering this civil support need to be as well coordinated as any military force. We know there is plenty of room for improvement. That is the thinking behind the pioneering civilian-military mission in Lashkar Gah.

Today, about half of Afghanistan’s children are in school. Infant mortality rates have tumbled. We are helping the Afghan government to focus on empowering its local governors to deliver services. Afghan, not international, contractors are increasingly being used to build roads, schools and health clinics.

Then there is the role of Pakistan, where the security situation has worsened in the past year and a porous 1,615-mile border provides a recurrent security headache. The past year has seen tragedy produce change. The assassination of Benazir Bhutto and the recent attack on the Marriott hotel in Islamabad have shown that Pakistani-based terrorism is a threat to Pakistan, not just a threat to the West. Asif Zardari, president of Pakistan, committed to me that he would make cooperation with the Afghan government (and India) a priority and he has been true to his word.

The role of the international community is not to wring its hands and go home, but to help the Pakistan government get a grip on its tribal areas, from which insurgents plan, recruit and arm for attacks in Afghanistan. This means doing better in neutralising the attacks from suicide bombers and roadside bombs. It means doing better on engaging the ordinary people on both sides of the Afghanistan-Pakistan border. It also means a massive economic effort with the help of the international community.

People sometimes ask how we expect to succeed when the Soviet Union failed with 200,000 troops in the 1980s. My answer is that we are not seeking to emulate the Soviet Union. We are not seeking to establish a colony or subjugate the will of the people.

Our cause is simple: to help Afghanistan make itself safe from the Taliban and, in the process, to make ourselves safer from Al-Qaeda. That requires enormous heroism from Afghans and their international partners. Yes, it is difficult. But it is not impossible.

David Miliband is foreign secretary.

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