It’s barely three years since I embarked on my walk across Afghanistan, just after the fall of the Taliban. It was a journey with quiet echoes of Scotland.

Badges of Scottish regiments are carved in the rock on the Pakistan-Afghan frontier. They dominate the Khyber Pass, through which the British Army of the Indus confidently marched in 1839 and down which Dr Brydon, the sole survivor, returned in 1842.

It was never clear to me what these Victorian boys from Highland villages thought they were doing as they carved the symbols into Afghan granite. When I passed them with Babur, my Afghan mastiff, I saw them as crude monuments of Empire. It was some time before I understood them better.

I had just walked 5,000 miles across Iran, Pakistan, India and Nepal, but I had not walked with a dog before. It was cold (-30C) and a brindle of black hairs stood up on Babur’s fawn coat.

He was one of the dogs of Ghor, “a breed so fine and powerful”, says a medieval Arab chronicler, “that each one of them has the strength and build of a lion”. I had seen mastiffs like him in Iraq carved into Assyrian rock friezes. But he reminded me most of the descriptions of the Celtic mastiffs who fought in the front line against the Romans in Britain.

I had looked at this area many times from aeroplane windows as I travelled back and forth between my birthplace in Hong Kong and my home in Scotland. But it had always been at night. The plane had passed the candelabras of city lights on the plains of India. From the Himalayas to Kurdistan, only occasional lights revealed we were not flying over a deserted ocean. I had never seen darkness so extensive.

Now I was walking through it in daylight. Over 19 months I was reducing the area to a more human scale: as though my legs were two callipers measuring with each step the distance between Scotland and Hong Kong.

As we entered the high mountains, we left behind the chiefs who travelled on horses, each followed by a line of armed clansmen. The heather and granite that reminded me of Ben Vorlich had given way to a more alien landscape. This was now the territory of Al-Qaeda, but it had been that of Scottish travellers such as “Walker” Stewart and Alexander Burnes. Burnes — who took leave from government service in his late twenties to travel up to Bokhara in central Asia — was the first to be killed in Kabul in 1842.

It was dry in Afghanistan and at 12,000ft the sky was an intense dark blue. The area was sparsely inhabited and on the 23rd day the only human we encountered before dusk was a frozen corpse.

My family have worked abroad for 150 years but always return home to Scotland. We have lived in Jamaica, Calcutta, Burma, China and Vietnam. My father was born in Edinburgh, but he went to India 15 years before he first visited England and from 1945 he worked in Asia for the British government.

I joined the Black Watch because I was brought up playing with Black Watch plastic soldiers on a prickly Malaysian lawn. Annie, my sister, was sent alone at 17 on the trans- Siberian train to Japan, my mother drove a Land Rover from Britain to Malaysia across Afghanistan in 1962 and Heather, my other sister, drove the same route in 1974.

I felt, however, there was something special about walking across Asia. I was moving at the same pace as the farmers at their ploughs and could feel the wind. Because I could walk only 20 to 25 miles a day, I spent my time in villages and towns that no tourist would visit and slept in 500 village homes. I was able to learn about rural communities and it was not always what I had expected.

One host who lived with his 10 children in two rooms, subsisting on a few acres of arid land, embarrassed me by saying: “You live a very hard life. I may be poor, but I return to my family every evening, whereas you have no home.”

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