Abu Hamza looked at me with his one good eye as we were introduced. “Masha’Allah, brother,” he said. “Can you meet me in the office after prayers?” “Of course,” I told him.

When prayers were finished I stood outside the office on the first floor of the Finsbury Park mosque in north London. Hamza approached with a young boy by his side. He gestured with his hook and the boy opened the door for him. We sat on the floor and Hamza asked the boy to bring us tea.

Hamza asked me which of the camps in Afghanistan I had been in, and I told him. Then I leant forward slightly. “I met someone you know,” I said in a conspiratorial voice. Hamza raised his brow just slightly.

“I trained with Assad Allah,” I told him. “He told me about the nitroglycerine, and how you lost your hands.” Hamza looked away. “Brother,” he whispered, not meeting my gaze, “please don’t share that story with anyone.”

As I was to learn later, Hamza claimed he had lost his hands defusing a landmine on the front lines in Afghanistan. I knew the real story.

Assad Allah was an enormous Algerian who had taught me how to handle explosives at the Darunta training camp near Jalalabad. With his green eyes and red hair, he looked like an Irish rugby player.

As a trainee mujahid I had learnt some basic things, such as how to set off an explosive using a watch or a mobile phone. But with Assad Allah we used complicated mathematics and chemistry, and the work required intense concentration.

We learnt to make every explosive from scratch: black powder, RDX, tetryl, TNT, dynamite, C2, C3, C4, Semtex, nitroglycerine, and so on. We learnt how to construct each of these from everyday products: corn syrup, hair dye, lemons, pencils, sugar, coffee, Epsom salts, mothballs, batteries, matches, paint, cleaning products, bleach, brake fluid, fertiliser, sand — even my own urine.

We learnt how to blow up a train, cars and buildings. We talked a lot about aeroplanes: Semtex was easiest to get on board, because it was almost impossible to detect, but it was hard to obtain so we learnt about liquid explosives.

We needed to know what to do instinctively. So we rehearsed the formulas over and over again until we could repeat them in our sleep. And every Sunday Assad Allah gave us a test to make sure we knew it. There was no joking around in his class. Any one of us could have killed the entire group with a small mistake.

One day Assad Allah told us about an accident that had occurred during his own explosives training. His group was learning how to make nitroglycerine, and one of the brothers wasn’t paying attention. He let the materials get hotter than he should have.

Luckily, the trainer saw the thermometer. “It’s going to explode!” he shouted.

There was a sink full of ice right next to the trainee, and he should have poured the materials on that to cool it down. But instead he rushed towards the door with the liquid timebomb in his hands. Just as he got outside, the mixture exploded. It blew both his hands straight off and destroyed one of his eyes.

Explore UK News

• Crime News

• Education News

• Health News

• Scotland News

Times Recommends

• Times Christmas appeal: Letter from the Editor
• Conferences — what a waste of money
• Schools supremo learns a painful lesson