For the Record. David Cameron

Taliban was because they seemed better at dispensing justice and ensuring order than the legitimate authorities. And corruption was so ingrained in the country’s culture that Karzai could never quite accept that we were there because we genuinely believed in the mission as part of an international coalition. In January 2012 I remember him asking me what was it – minerals? mining rights? – that we really wanted from Afghanistan.

      He could be hard work. He would criticise the activities of British and American troops, even though they were making extraordinary sacrifices and were essential for his regime’s survival. And he found it too easy to play the nationalist card and blame all his problems on Pakistan.

      But there was enough there for me to be able to use the relationship I had built up, and the fact that the Pakistanis trusted us more than the Americans, to help build the trust between Afghans and Pakistanis.

      The high-water mark of my efforts came at the Chequers summit in 2013 when Karzai and President Asif Ali Zardari of Pakistan spent two days in talks. They slept in adjoining bedrooms, each with a guard outside sitting ramrod-straight and wide awake in his chair. I came downstairs the next morning to find the two presidents joking about which of them had been snoring the loudest.

      We agreed a series of small steps to build confidence: publicly praising each other’s leadership; agreeing visits to each other’s countries; and – crucially – recognising that the security of one was the security of the other.

      We aimed to move on to talk about border security and the import­ance of dealing with terrorist safe havens on both sides of the Durand Line (the controversial border between the two countries). We wanted to get some of their military and intelligence personnel to sit together and work together – even suggesting joint patrols. A further series of coordinated steps would then follow to help deliver a peace process: the release from Pakistani custody of potential Taliban peacemakers so they could carry out talks, hints that Afghanistan would consider constitutional reforms, and so on.

But Karzai couldn’t bring himself to trust Pakistan. Zardari was often willing, but as we know, it is really the military that makes the key decisions.

      The Americans were supportive and appreciative of our efforts. They took up the cudgels for contacts with the Taliban, but ultimately the distance between the two sides, and their half-heartedness about a compromise, was too great to make meaningful progress.

      This is the agenda I most wish had come off. But I am convinced that it remains crucial today, and that it can be done.

      So, for all the blood spilt and treasure spent, was Britain’s involvement in the Afghan war worth it? Historians say it’s too early to say. It is incredibly depressing whenever the country slips back. Sangin is back in Taliban hands. Their flag flies over Musa Qala. Opium fields still stretch across Helmand. These are painful things to write.

      But at the same time, in 2014 Afghanistan saw its first peaceful, democratic transfer of power, to the anti-corruption academic Ashraf Ghani. It now has its own police force and national army. And more than that. By 2011, 85 per cent of the country had access to basic med­-ical care, compared to 9 per cent under the Taliban. Seven million more children were in school compared to one million in 2001. A third of them were girls. Not a single girl went to school in the Taliban years. As long as we go on funding the Afghan army and police (and the inter­national community remains committed to this), the Taliban is unlikely to win the whole country, and terrorists cannot get the same foothold they had before.

      The agenda is still the same. The Afghan government needs to deliver for all its people. It needs to find a way of bringing at least some elements of the Taliban into the legitimate political sphere. It will only do this if it forges a trusting partnership with Pakistan, where both accept that allowing safe havens on either side of the border for terrorists will end up destroying them both.

      The difference now is that our troops are not exposed to the daily risk they once were. Arguably, it will be easier now for some sort of deal to be done because the provocative presence of foreign troops on Afghan soil is so much less.

      The prevailing views are that this war was either doomed to fail or that it should have been pushed harder. I believe there is a third category, where you do the right thing and keep doing it, but it takes a very, very long time before you achieve stable and lasting success.

Samuel Beckett said, ‘Fail again. Fail better.’ Foreign troops could only ever provide a breathing space for a legitimate Afghan government to get its act together and deal with the fundamental issues.

      Delivering security and some semblance of uncorrupt administration; getting the relationship between Afghanistan and Pakistan right; achieving a political settlement which demonstrates that all Afghans are welcome. I believe all these things are achievable. The story isn’t over.

      Afghanistan brought me into close contact with the UK’s military chiefs. While there were robust arguments and discussions, they were generally good-natured. However, my relationship with them would come under greater strain when we had to discuss another intractable challenge: how to make sense of the UK’s defence budget in an age of austerity.

      I had read widely about the history of military top brass interacting with those at the top table of government – particularly the blazing rows between Churchill and General Alan Brooke in the rooms I was now so familiar with in Downing Street. I have huge respect for the chiefs of staff who head up the army, navy, air force and the armed forces as a whole. But PMs need to build up their own expertise. Like all my predecessors since James Callaghan, I didn’t have a military background, so I decided to hire a senior military adviser to be in my private office.