Foreign Parts: With floppy hats, hiking boots and sticks, the British carry on up the Panjshir Valley

In the CIA's headquarters in Langley, Virginia, there is an agent - or perhaps a team of agents - whose job is probably to analyse photographs that stream in from American spy satellites over Afghanistan.

Their attention will be particularly trained on the south and eastern areas in the hope of spotting their naggingly persistent enemies - the Taliban, al-Qa'ida and an assortment of other guerrillas - moving around the mountains.

They surely dream of one day seeing Osama bin Laden himself, picking his way through the gullies, sallow and exhausted from life on the run.

Had the same agents switched their attention northwards this week, a rare sight would have flickered on to their screens. Zooming in, they would have detected a line of people, perhaps by now divided into two groups, moving by foot up the Panjshir Valley, which climbs up towards the mountains of the Hindu Kush.

Zooming in still further, they would have seen that the column bore little resemblance to the bearded men of the Taliban, but was extraordinary all the same. It had floppy hats - protection against the brilliant sun - spotted neck-scarves, sticks and sturdy walking boots.

It had a surprising number of snowy-haired people, a patrician flavour, and included an elderly but still glamorous dowager, Lady Pamela Egremont, who is not far shy of 80, riding on a horse. It also contained a rugged face that was for years known to every British television viewer.

Escorted by Afghan guides, 25 people, mostly Britons, set off this week on expedition up the 93-mile valley, crossing the route used by Alexander the Great during his northbound trek in 330BC and travelling along what later became one of the great trading routes from Central Asia to India.

They have been summoned to this place - one of the most beautiful in the region - by the former ITN newsreader, author and foreign correspondent Sandy Gall. This is territory he knows well: in 1982, he spent two months in the valley reporting resistance by the CIA-funded, Pakistan-backed "mujahedin" to the Soviet forces, who invaded Afghan-istan in 1979 but never managed to enforce a full occupation. He has regularly returned.

I watched the party draw out of the capital, Kabul, departing in a convoy of vehicles, apparently unworried by venturing into the hinterland of a country that is still far from stable - although, it must be said, the Panjshir Valley is one of the safer areas. They set off a day late because Afghanistan's national airline, Ariana - one of the most eccentric in the world - had sent their luggage to Sharjah, in the United Arab Emirates. Despite this, they had the calm air of people embarking on a week of strolls along the Cornish coastal footpath. Being British, they are, of course, on a sponsored walk.

What is it about the British and Afghanistan? Historically, their experience in this part of the world has been punctuated by disasters. They invaded Kabul in 1839 and were defeated - only one of the 16,000 troops and camp followers who withdrew from the city three years later managed to survive. Later that year, they returned and exacted revenge by blowing up the bazaar. Three decades later the imperial forces were back again, and defeated again.

Yet the place still seduces. Lady Pamela has had a lifetime's fascination with the place. "I guess," ventured one of the walkers, John Fixsen, a 69-year-old orthopaedic surgeon, "that in the end we are all just rather crazy." This party, at least, is there for a good cause.

The walk marks the 20th anniversary of Sandy Gall's Afghanistan Appeal, which he founded in 1983 shortly after his first stint in the war zone the year before. His advancing years, he's 75, do not seem to have diminished the enthusiasm he throws into this work, visiting Afghanistan at least once a year, although he is "slightly less optimistic" about the country's prospects, given the resurgence of the Taliban in the south. "People tell me that the government isn't getting its message across, but I think the Afghans will probably muddle through," he said.

The walkers will raise £50,000 to support the charity's clinics in Afghanistan, which treat the disabled - children crippled by polio and landmines. Afghanistan, fought over for more than two decades, is the most heavily mined country in the world; the Americans did their part by dropping cluster bombs in the assault against the Taliban nearly two years ago. You cannot but notice the number of beggars on the capital's street who are missing a leg. They are the lucky ones.