In May 2007, when I was told I had the part of Jesus, I’d be lying if I said there weren’t moments when I didn’t fill up with a sense of dread. How on earth was I going to play probably the most famous man in history? How would I act out the last days of a man we are still trying to understand over 2,000 years later? Armed with Frank Deasy’s script, I began reading the Gospels, research papers, medical documents, endless books and prayers. I soon realised, though, that the only way I could even begin to understand this whole thing was to relate to Jesus as a human being — with all the weaknesses and strengths of a human being. As a man the same age as me who was now being sentenced to death for his beliefs.

At the end of August I flew out to Marrakesh with the rest of the cast and crew to begin shooting. We were arriving at the hottest time of the year, so the first thing to greet us was the fierce white heat of the midday sun. A five-hour car journey took us along desert roads and through the unforgiving wilderness of the Atlas mountains. We were heading for the town of Ouarzazate, often called the gateway to the Sahara. This was to be our base for the next two months.

Filming was to take place at several locations in and around Ouarzazate — including the studio that was used for Gladiator, a huge desert area encased by high walls. After three months of mental and emotional preparation, it was also now the physical demands of the role which were to test me. And without a doubt, the one experience which would exceed all others was the Crucifixion scene. Its location was a totally exposed, rugged, mountainous area out of town. But our first two attempts were thwarted by freak downpours and screaming winds that sent everything from sand to tents flying. Filming was impossible. By the night before our third attempt, tensions were high, and I was filled with trepidation.

I’d only slept a little when my alarm went off at 3.30am. Outside it was pitch-black and temperatures had plummeted when I was taken to the studio to begin make-up. Five hours later I emerged in a loincloth. My feet and legs were blistered, bloodied and bruised. My back now looked like it had been struck many times by a whip with a tail of small lead balls that had ripped my skin and hooked into my flesh — a form of torture the Romans liked to use. My upper body and face had been smeared with a cold, sugary liquid that looked like blood which had been left to congeal around my eyes and hair. The crown of thorns looked like it was piercing the skin on my forehead.

By now it was around 8.30am, the sun was coming up and the torrential rain had given way to vast blue skies. Filming began a short distance from the Crucifixion site. The heat was already making me sweat and the high altitudes were taking their toll, too. At the forefront of my mind, though, was the pain and exhaustion I could only imagine Jesus feeling as he stumbled with his cross through the narrow, crowded streets of Jerusalem up to Golgotha. Nailing my arms to the cross was made possible by a prosthetics expert using special clips, fake nails and latex made to look like blood-drenched skin. Then I had to bend my knees to the right, resting my feet on an iron peg, while a second peg allowed me to rest one bum cheek. Hanging there with your arms stretched out and your knees bent was one of the most common ways used to crucify people by the Romans. A twisted body was much harder to push upright than a straight one, so it became harder and harder to breathe in and out. If you didn’t then suffocate to death by the end of the day, they would break your legs, and the agony of that would kill you.

Being lifted up on a 13ft cross by the crew was as shocking as it was surreal. It began jerkily, and I could feel the weight on my arms increasing as the pole initially rocked from side to side. A shaft had been dug into the ground and the cross dropped into it with such abruptness that it sent a painful spasm up my spine. I remember feeling like someone in a car crash — everything seemed to happen in slow motion. The sun was absolutely blinding, but I had to keep facing upwards. The director had positioned a camera above my head to capture the agony on Jesus’s face and the moment when he utters his last words.

The scene took three days, and although I’d only been up on the cross for minutes at a time, my arms were still numb when I returned to London. It was such an intense and all-consuming experience that it took some time to get it out of my system. Luckily, there was probably no better way of exorcising any fantasies I still had of being the son of God than by accepting the lead role in Stephen Adly Guirgis’s black comedy, The Last Days of Judas Iscariot. I guess for every good guy, there’s always a bad guy waiting to take centre stage.

The Passion is released on DVD tomorrow

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