The ageing Nissan 4x4 is racing and rattling through the potholed roads of the Mansour district of Baghdad. The young driver, his hand glued to the horn, is taking instructions from his “boss” in the front passenger seat. Frantic exchanges of Arab male voices fill the car.

As we screech around a bend opposite the remains of one of Saddam’s palaces, the road ahead is gridlocked with three lanes of morning rush-hour traffic. The boss (who wishes to remain anonymous) takes immediate action: he pulls out his Heckler & Koch 9mm pistol and squeezes his upper body through the window. With the gun in his hand we hurtle towards the oncoming traffic. Welcome to minicabs, Baghdad style, or as close as you can get to them in a war-torn city.

As a photographer, I have made thousands of car journeys in Iraq over the past five years, which can by turns be boring, frustrating or terrifying, but even by Baghdad’s standards this one stands out.

The dangers are well known for journalists operating in this city. Before you even get in a car the journey must be meticulously mapped out - every potential threat has to be taken into account, and this takes time. You must find out which roads are hot, or “red routes” as the military call them, because of recent IEDs (improvised explosive devices, or roadside bombs), suicide bombings (by car or on foot) and kidnappings and attacks by militia gunmen. The list is long and sobering.

Even when you do get in a car, it will always be partially armour-plated and driven by a trusted aide. But on this occasion none of these things had happened. In the time-honoured tradition of Iraq, somewhere there had been a cockup.

Earlier in the day I should have left the relatively secure compound where I was staying with my wife Hala Jaber, the Sunday Times foreign correspondent. We were spending a few days on assignment with a well known politician, who had offered to take us on a couple of trips outside the city with his armoured convoy. That day he was heading to Abu Ghraib, the rural area infamous for its prison. I would be taking photographs and videoing the trip.

But the convoy had left without us. Under normal circumstances that would have been irritating but nothing more: we would have sat it out in the compound and waited for another convoy. However, when the politician realised we were not with his group, he ordered his people to make sure we join him. The problem was that they would not be able to wait long for us to catch up: they were at Assassins’ Gate, the entrance to the “safe” green zone, so called because it is where suicide bombers strike at workers queueing up to enter.

At that time of day, the journey of about four miles from our compound to Assassins’ Gate would take 30-40 minutes. And so the order came down to get us there in 10 minutes flat.

We are back in the car, with two wheels on the central reservation and the boss, an aide to the politician, threatening to shoot any driver too slow to pull over. I have decided that if I am going to die in a crash then at least I am going to record it on video. I look at Hala – her nails are embedded in the imitation leather of the driver’s headrest.

Then, just as I think things can’t get any worse, they do. Out of the cracked windscreen I spot a roadblock ahead. It is not just roadside bombs and the threat of random attack that make driving in Iraq perilous. You must also contend with the numerous checkpoints that line most main thoroughfares. These may be manned by the Iraqi police or army, a ragtag collection of militia or US marines. In many ways the checkpoints are most dangerous for westerners: the minute the car stops you are vulnerable, but if you don’t stop you run the risk of the soldiers opening fire on your car. It is the ultimate Catch22.

At this point the boss went into meltdown. As we passed a bus, I could see an old Honda in front of us whose driver had clearly not seen or heard us approaching his rear. I caught the sound of the boss pulling back the slide mechanism of his pistol. A gunshot rang out and the Honda swiftly swerved to the right as we powered on.

There are many things that it is inadvisable to do when approaching a checkpoint manned by heavily armed personnel, especially at speed in an unmarked car. But firing a pistol out of the window probably comes top.

We passed the first soldier about 50 yards from the main checkpoint. He was Iraqi army. This was a welcome sign; if he had been American there is a good chance we wouldn’t have made it this far: “Official press release: at 08.54 US marines at checkpoint 711 observed a rusting, white, unmarked 4x4 heading towards them at speed. On the passenger side a male of Arab appearance in civilian clothes was hanging out of the window pointing a pistol and shouting threats in Arabic. After warning shots and appeals for the vehicle to stop were ignored, the order was given to open fire. All four occupants of the vehicle were pronounced dead at the scene. We would advise all journalists in Baghdad, for their own safety, not to travel in local, unlicensed minicabs.”

By now, though, we were close to the main checkpoint. “Yalla, yalla,” (“Hurry, hurry”) the boss was still shouting at the driver. Outside, soldiers began shouting, “Stop!” in Arabic. Mercifully we did. The soldiers wanted to know why the boss had fired his gun.

The boss gave his answer: “We had been stuck behind him for a f****** hour! What else do you want me to do?” There was a pause. The soldier shrugged and, as if it was a perfectly reasonable answer, waved us through.

On the other side, the rear of the armoured convoy comes into sight a couple of hundred yards later and we slowly come to a stop in between the sixth and seventh vehicles. Hala and I look at each other and laugh nervously. The boss stares impassively at us through his Gucci shades: we had made it.

The next time I am in a minicab in London and the driver gets lost or we are stuck in heavy congestion, I will think of that recent journey in Baghdad. And I won’t think how lucky I am. I will think how useful it would be to have that boss sitting in the front seat.

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