Two years ago, when I last travelled up the Salang, the villages were deserted and in ruins, while the military posts were intact. Now it is the other way round, and Mr Porter, 32, can claim much of the credit. From their base at Jabal os Saraj, the former Royal Marines officer and his Afghan teams have cleared hundreds of explosive devices from the slopes overlooking the most strategic road in the country, allowing people to return.
Travelling north from the shattered capital, Kabul, we passed through villages celebrating the end of Ramadan, the Muslim month of fasting. Brightly-dressed little girls, their faces plastered in make-up, were giggling as they rode a home- made wooden Ferris wheel, cranked by hand. All around them, however, were crumbling mud walls and untended fields.
By the side of the road was a memorial to three of Mr Porter's colleagues from Halo Trust, the British charity dedicated to clearing mines. Tim Goggs, Julian Gregson and Shah Mohamed died in July 1992 when a booby-trap ignited the tank they were using to clear devices. The blackened vehicle is still in place, about 100 yards from the memorial: as we examined it, shells exploded on a mountain top nearby.
It was a superfluous reminder that Afghanistan remains at war, two years after the fall of the Communists. The villages of the southern Salang are an exception, and their peace is fragile. After climbing past the snowline and emerging from the world's highest tunnel at the crest of the Salang pass, nearly 12,000 feet up, we were halted by government forces. There was fighting a few miles further on.
A freezing wind drove snow flurries into the faces of Hizbe Islami prisoners, who were being encouraged to unload a truck with kicks and rifle-butts. A government soldier, who had taken bullets in the neck and shoulder, stood by waiting for a lift to hospital as Mr Porter negotiated with the commander.
Halo Trust has another base at Pul-i-Khumri, a stronghold of Afghanistan's Ismaili Muslim minority. During 13 years of mujahedin war against the Communist regime, the Ismailis were courted by both sides, and extended their influence over the northern end of the Salang. The ruling Naseri family, however, recently threw in its lot with the anti-government alliance, which appears to have been a disastrous mistake: yesterday the government said it had taken Khenjan, and the opposition was reported to be digging in near Dowshi. Pul-i-Khumri was bombed a few days ago.
The fighting has prevented traffic moving through the Salang for well over a week, and Mr Porter's chances of bringing mine-disposal equipment to Pul-i-Khumri in the near future look dim. 'Mine clearing is a grindingly boring but dangerous job, which requires you to maintain your concentration in summer temperatures of up to 110 degrees, but basically it is straightforward,' he said. 'The difficult part is establishing links with local communities, dealing with armed factions and above all ensuring that you are seen to be neutral.'
Halo Trust is the only de-mining body in the country run by expatriates. Most work is carried out by Afghan groups with money from the EU and the United Nations. Last year they cleared 29 square kilometres, but there are 5 million devices remaining. 'If we carry on it has been estimated that we could restore normal life to most villages in three to five years,' said Mr Porter. 'But we cannot guarantee that the land will not be mined again.'