Osama Bin Laden, who had been sitting cross-legged on a carpet, placed his Kalashnikov rifle on the ground and got up. He came towards me with a warm smile that turned into barely repressed laughter as he took in the way I was dressed.

I had been kitted out in baggy trousers, a long shirt and a turban for my clandestine journey to his hideout in southern Afghanistan. The turban in particular made me feel self-conscious, as I had never worn such a thing in my life.

I spent three days with Bin Laden in Tora Bora, the only western-based journalist to spend such a significant amount of time with him, before or since. I talked at length to him, slept next to him in his cave and shared his modest food.

Listening to him during that visit 10 years ago I realised he was no ordinary figure, but it didn’t occur to me for one moment that this polite, soft-spoken, smiling and apparently gentle person would become the world’s most dangerous man, terrorising western capitals, inflicting hundreds of billions of dollars’ worth of damage on the United States, threatening its economic stability and embroiling it in wars in Afghanistan and Iraq.

As I had been eating so badly since coming to Afghanistan I was looking forward to our first meal. I’d imagined we would feast on roast deer or goat. When I saw what was available at the Eagle’s Nest, as his base was called, I thought chicken was perhaps a more likely dish.

It was still a great surprise to discover that dinner on the first night consisted of Arab-style potato chips soaking in cottonseed oil; a plate of fried eggs; salty cheese of a variety long extinct even in the villages of upper Egypt; and a bread bun that must have been kneaded with sand, as my teeth screeched and ground whenever I chewed it.

After a few bites I pretended that I did not usually eat dinner for health reasons.

Another meal featured Bin Laden’s favourite, bread with yogurt and rice, served with potatoes cooked in tomato sauce. Animal fat floated on the surface, and I could hardly force it down my throat. Afterwards I was sick under a pine tree outside the cave.

I was puzzled by Bin Laden’s chosen path. What motivates this man, from a well-known and honourable family in possession of billions, to lead such a comfortless life in these inhospitable and dangerous mountains, awaiting attack, capture or death at any moment, hunted by so many regimes?

We spoke about his wealth, and while he avoided saying exactly how much he was worth he acknowledged he still managed an extensive investment portfolio through a complex network of secret contacts. But this wealth, he said, was for the umma (the global Islamic community).

“It is the duty of the umma as a whole to commit its wealth to the struggle,” he said. “The umma is connected like an electric current.” (Surprising imagery for a man who would wish to take us back 1,500 years.) I discovered that, in contrast with the primitive accommodation, the base was well equipped with computers and up-to-the-minute communications equipment. Bin Laden had access to the internet, which was not then ubiquitous as it is now, and said: “These days the world is becoming like a small village.”

This modernity was quite at odds with the austerity recommended by the more extreme forms of Islamic fundamentalism and in particular that of his hosts, the Taliban. One of his aides laughed and said the base was “a republic within a republic”.

The next day Bin Laden took me on a guided tour, sporting the Kalashnikov so dear to him. (He told me it had belonged to a Soviet general killed in one of the Afghan jihad battles.) We walked through the trees and he explained that he loved mountains. “I would rather die than live in a European state,” he declared.