Then wham! Some heavy object flew down from the side and slammed into the back of my right leg with a terrific blow. Jesus, I thought, a meteorite. No – a falling human body. The impact knocked me out of the posture I’d been working to hold. Worse, it knocked my bergen from its central position behind my knees and pushed it over to the outside of my left leg. In an instant I was destabilised, still face-down, but spinning.

I knew I was in the shit. A spin is the worst thing that can happen to a free-faller, the fate everybody dreads. If one starts on its own it may wind up slowly, and you stand some chance of correcting it. But after an impact of that kind, you’re away. The combination of momentum and air pressure is so ferocious that you’re rotating like a propeller, and that’s you gone.

I struggled with hands, arms and legs to adjust my posture, to regain control. But whatever I did, I just spun faster. For the first few seconds my mind stayed clear. Maybe one of the lads will see what’s happening, I thought. Maybe someone will steer in to give me a hand. Then I realised, No, they can’t. This is too violent. If anyone tried to make contact I’d smash them, or they’d smash me. We’d break limbs, knock each other out. If they’ve got any sense, they’ve pulled off to a safe distance. I’m on my own.

All this went through my mind in a flash. Then I thought, I’m going to have to cut my bergen away. Pull the cord to dump it. Lose all my kit. But by the time I’d taken that decision it had become physically impossible. The centrifugal force of the spin was so great I couldn’t get my hands anywhere near my body. No way could I reach my knife, still in its sheath on my right leg. My arms were locked straight out, hands and fingers throbbing with the pressure of blood forced into them. They felt as if the skin was going to burst. My head seemed to be swelling, too, the skin round my eyes bulging, vision deteriorating. Geordie Sharp, I told myself, this is it. During your career in special forces you’ve got out of plenty of tight corners, but this time, finally, you’re fucked.

I wasn’t exactly frightened; everything had happened so fast there was no time to worry. I just seemed to accept that fate had got me by the short-and-curlies, and I was going in at 125mph. Obliteration, I thought. Fair enough.