It had begun out in the spring sunshine, on the streets of Gaza City. A saloon car had suddenly surged past mine, and then pulled up, forcing me to stop. A young man emerged from the passenger side and pointed a pistol at me. The figure with the pistol and another gunman forced me into their car, and as we sped off I was made to lie on the back seat. A hood had been shoved over my face, but through it I could see the sun flickering between the tower blocks. I could tell that we were heading south and east, towards the city’s rougher neighbourhoods.

Late on the first night of my captivity, the door opened. Its frame was filled by a tall figure in a long white robe. He stood for a moment, looking down at me – swathed in a red-chequered headdress that completely masked his face. The Jihadi leader had arrived. “Alan Johnston,” he said in English. “We know everything.”

Mostly the voice emerging from the mask was calm, and even kindly. He said that I would not be killed. That I would be treated well, in keeping with Islamic codes of conduct towards prisoners. Crucially, he said that I would eventually be allowed to leave. I asked when, but he just said, “when the time is right.”

Later I was woken by two men coming into the room. They handcuffed me and put the black hood back over my head, and led me slowly out into the cold of the night. There was no word of explanation, and as my mind searched for one in that terrifying moment of uncertainty, I feared, as I walked into the darkness, that I might be going to my death. That I was being taken somewhere to be shot.

But the tension eased as I began to realise that the men were only moving me to another building.

I had been stripped of my watch, and could only tell the time by the passage of the sun, and the five calls to prayer from nearby mosques. I had had to throw away my disposable contact lenses on the first day, and my eyes are very weak. And so, in this blurred, empty room I began to try to come to terms with the disaster that had engulfed me.

Almost all that Britain had left in Gaza was the BBC. And in the BBC, there was only one British citizen, me. And the Jihadis had me, like a bird in a cage. I thought of the Western hostages who had been held for years in Beirut in the 1980s, and wondered if their fate might now be mine.

The first crisis came in the form of a bout of illness. My European stomach could not cope either with what I was eating, or the dirty water. Soon I could feel a swelling just below my ribs, and there were many trips to the small, foul-smelling toilet attached to my room, where the floor was always awash with water.

I asked just for a plate of chips each day, and for my water to be boiled. And those simple elements, along with bread, tomatoes, some fruit and later eggs became the basis of my rather dull but safe two meals a day. There was, though, never quite enough food, and I eventually lost 10kg (22lb). I was sure that, if it came to it, the Army of Islam would just let me fade away slowly rather than call off the kidnap because I was sick.

Desperate for some distraction to ease the psychological pressure, I had repeatedly asked for a radio, and amazingly [one night] a guard brought one into my room. Suddenly I had a link with the outside world. A voice in my cell, and something to listen to other than my own frightening thoughts.

And through the radio I became aware of the extraordinary, worldwide campaign that the BBC was mobilising on my behalf. It was an enormous psychological boost.

But the radio also brought dreadful news. In those calm, measured tones of the BBC, I heard reports of a claim that I had been executed. It was a shocking moment. I had been declared dead. But of course, I knew that I was far from dead, and after a few minutes I could not help recalling that famous Mark Twain line: “Reports of my death are exaggerated.”

I was worried though, that perhaps the announcement of my execution was just a little premature. I was sure that if I was to be put to death, the act would be video-taped in the style of Jihadi executions in Iraq.

If that was to be the last image my family and the world was to have of me – if at all possible – I did not want it to be one of a weeping, pleading, broken man. So through that long night, I lay listening to every sound that might signal the coming of my assassins, and tried to gather the strength that I would need if the worst were to happen.

A few weeks later my guard barged into my room with a set of manacles. My wrists and ankles were chained together. He told me that it was being decided whether I should be put to death in the days ahead. If that was to happen, he said, my throat would be cut with a knife.

I did not quite believe the threat, but again, I had to prepare myself for the worst. I chose to rehearse in my mind exactly what might happen, hoping that somehow that would make the lead-up to any execution a little less shocking, and hoping that that might make it easier to preserve some kind of dignity in my final moments. But mercifully, the crisis passed.

Through all this I gradually came to know my guards. One of them, a man in his mid-twenties called Khamees, with a dark, quite handsome face, would be with me almost every day. Right through to the kidnap’s frightening climax.

Occasionally he would let me go through to his room and watch television for an hour or two. And one day he allowed me to see my parents make a televised appeal for my release. After worrying about them so much, it was a vast relief to see my father make a powerful and dignified address. And although my mother did not speak, when I looked into her eyes I was somehow sure that she too had the strength to cope.

There were moments when Khamees would be friendly, when we would talk a little about Gaza, and about politics or Islam. But mostly I will remember Khamees as a dark and moody figure. A number of times tiny things sent him into frightening rages that I came to dread. And when he smashed me in the face in the final moments of the kidnap, I felt that with Khamees, perhaps, all along violence had never been far below the surface.

Whatever else it was, my Gazan incarceration was not what Iraqi prisoners had been forced to endure at Abu Ghraib jail. It was not the Russian gulag, and it certainly was not the Nazi death camps.

In its search for inspiration, my mind took me down what may sound to you like some rather strange paths. For me, as impressive as any story of endurance, is that of the British explorer, Ernest Shackleton. After his ship was crushed by the Antarctic ice nearly a century ago, he took a tiny lifeboat and set out across the great wastes of the stormy Southern Ocean. He aimed for an almost unimaginably small island far beyond his horizon, and eventually he reached it.

And in my prison, I felt that I needed some kind of mental lifeboat, to help me cross the great ocean of time that lay before me, aiming for that almost unimaginable moment far beyond my horizon when I might somehow go free.

Eventually Gaza’s violent politics suddenly shifted against my kidnappers. The powerful Hamas and Fatah factions began a fight to the death.

Eventually Hamas managed to seize complete control. For the first time, my captors seemed shaken, and uncertain – but they had a plan.

Khamees came into my room with a plain, black briefcase, of a kind that you might see any accountant carry on the London underground. He opened it to reveal a suicide bomber’s vest, with panels of explosives that closed tight around my stomach as I pulled it on. The message I had to give via a video camera – dressed in my deadly contraption – was that if there was an attack, I too would die.

But Hamas was closing in, and the Army of Islam prepared for a showdown.

Then suddenly, late one night, I was taken downstairs. A hood was put over my head, and I was led stumbling out into the darkness as members of the gang began to hit me and slam me against walls and the side of a car, before I was shoved into its back seat. The kidnappers and the powerful clan that was protecting them, had agreed to deliver me up in return for their survival. But I did not know that, as the car began to move slowly towards the Hamas lines, and the most terrifying ride of my life began.

My guards, with their Kalashnikov rifles on each side of me, were screaming angry – furious, no doubt, at the failure of the kidnap and scared, perhaps, that Hamas would kill them anyway, whatever the deal. Khamees struck at my head, and I could taste blood in my mouth. At one of the checkpoints, through the wool of my mask, I could see the muzzle of a rifle inches from my eye and I knew that the guard on my right was roaring that he would put a bullet in my brain if the Hamas men did not back off.

Eventually we came to a halt, and Khamees dragged me out into the road. As we turned a corner, there, standing in a garden, was my old friend and colleague, Fayed Abu Shamalla, of the BBC Arabic service. Only then did I know that my kidnap was over, and that I was free.

Sometimes I dream that I am in captivity again, and I cannot tell you how good it is to wake and gradually realise that, actually, I am free. But the nightmares come less frequently now. And although psychologists might say that these are still quite early days, I very much believe that I am going to be fine.

And the kidnap’s legacy is not all bad. It was a kind of dark education. I lived through things which before I would have struggled to imagine and maybe, in the end, I will be stronger for that. I have gained a deeper sense of the value of freedom. Perhaps only if you have ever been some kind of prisoner, can you truly understand its worth.

Even now, more than three months after I was freed, it can still seem faintly magical to do the simplest things, like walk down a street in the sunshine, or sit in a caf� with a newspaper.

And in my captivity in Gaza, I learnt again that oldest of lessons. That in life, all that really, really matters, is the people you love.