The Americans didn't have a Black Hawk to spare for the five-minute hop into the Green Zone, so we were going to have to drive it. This is the bit Jeremy swore he'd never do. When you're asked where you draw the line, this is the place to start drawing. Nobody drives into Baghdad if they've not been given a direct order. Even our minder, Wing Co Willox, has never done it.

We're definitely not up for this, so we go and have coffee in the Green Bean, the American army's version of Starbucks in a Portakabin that hunkers down behind prefab blast walls, "proud to serve" skinny macchiatos in Iraq, Afghanistan, Uzbekistan and any other stan that needs shock, awe and caffeine. A pair of skinny Iraqis work their way through the fast of Ramadan, serving homesick grunts airlifted blueberry muffins.

An officer from the Irish Fusiliers tips up, all perky green hackle and steely Ulster confidence. "There's absolutely nothing to worry about," he says, and instantly you know there's nothing to worry about because worry is too weedy and snivelly a civvy word for what we ought to be feeling. He doesn't mention that they've just shot their way in here or that they sent an unmanned drone down the route to check it out first.

We wear body armour and helmets in the car. This doesn't make you feel safer, just an oven-ready prat. Our folksy safety briefing boils down to: if by the merest chance anything worrying occurs, close your eyes, put your fingers in your ears and pretend to be a prayer mat.

We travel in a small convoy. Two armour-plated Range Rovers with what they call top cover: Land Rover snatch vehicles in front and behind with a pair of soldiers sticking out the top. Being a human turret is a bad job. "We do this a bit faster than the Americans," a lance corporal tells me as we gingerly pull out of the airport perimeter. That's because the Americans do it in tanks. This road is code-named Route Irish. Guinness World Records has just authoritatively announced that Baghdad is the worst place in the world. Presumably in a photo finish with Stow-on-the-Wold. This 25-minute stretch of blasted tarmac from the airport to the Green Zone is, as Jeremy might say, the most dangerous drive — in the world.

Unsurprisingly, there's not much traffic. Surprisingly, there is some. "It's relative," says the corporal. "The worst road in the world is the one the bus runs you over on. The rest are a doddle."

The fusiliers drive with a practised authority, zigzagging, never contravening each other's line of fire. The top-cover soldiers swivel with their rifles to their shoulders, eyes pressed to the sights. There is a purposeful tension, a tunnel-visioned concentration. Going under bridges and flyovers is the worst: they traverse the parapets with a gaunt expectation and I begin to see everything in hyper-real detail. Every pile of rubbish and burnt-out car waits to jump out at us screaming "God is great" in a flash of hot light.

The convoy slows down; not a good thing.

A car ahead crawls to a stop. The soldiers emphatically signal to it to move on. Maybe it's someone taking a moment to tell God to put the kettle on; maybe it's just a clapped-out motor that's stalled. Army convoys, particularly the American and private-contractor ones, are really dangerous for Iraqis. Lethal force is everyone's first and last option. On a slip road, lopsided purposeful Toyotas packed with grim men seem to race to catch us. Perhaps they just want to get home to break their fast. Perhaps not.

Baghdad looks like it's been beaten senseless, stamped on, bitten, battered and clawed; ugly and dirty, its gouged and grated walls ripped off, windows flapping, ceilings propped on floors. The thudded buildings look like rotten teeth in the receding gums of streets full of twisted flotsam, bent lampposts, tangled railings and pools of slime, all of it coated in ground concrete dust. But it also seems surprisingly familiar, like a hot estate from a suburb of Detroit or Dundee. The journey takes longer than War and Peace. So I try and think about other stuff — like what's in it for female suicide bombers? The promise of 70 adolescent virgin blokes all sniggering to give you a premature seeing-to in heaven doesn't seem like much of an incentive. And then I'm back thinking about the increasing sophistication of roadside bombs. The Land Rovers carry secret wizardry that foils radio triggers made from phones or electric car keys, but now the locals are using infrared trips and the bombs are shaped chargers, a cone lined with copper or a metal with a low melting point covered in explosives. When detonated it forms a directed stream of molten shrapnel that'll go through a battle tank. There's no armour that will protect you from being kebabbed.

And then I think about the fact that the biggest helmet available fits on Jeremy's head like a little blue office-party joke hat, and that now he's facing his deepest fear (that he will cry like a girl when they video him having his head cut off with a bread knife to the soundtrack of Stairway to Heaven) looking like an unnatural cross between Obelix and the Elephant Man.

The convoy gets to the first of the Green Zone's many checkpoints and the Wing Co sighs with heartfelt relief. I realise we haven't spoken a word. In the other car, apparently, Jeremy hasn't drawn breath. We deal with fear in different ways. Silently I believe that if I see everything it'll be all right. He has to say everything.