WHILE reporting from the battlefront during the US-led invasion of Afghanistan in late 2001, James Meek asked a mujahideen commander of the Northern Alliance why his men were not firing on a small convoy of Taliban supply trucks in the distance. The commander had his reasons, but took the question as an insult and ordered an artillery strike. "They missed," says Meek, six years later, in a noisy Soho teahouse. "But not by much."He wrote about the incident at the time, in his capacity as a journalist.

He has written about it again, in his capacity as a novelist. His new book, We Are Now Beginning Our Descent, replays that scene differently, as the rockets find their target, and the protagonist, Adam Kellas, watches tiny figures in flames across the desert while talking to his mother in the UK via satellite phone.

"Your imagination steps in," says Meek. "What would that be like? What would it mean to me if I had been implicated in some way?" He is not Kellas, and vice versa; nor is the novel, as he puts it, "a guide to Meek, not that anyone would want such a thing". But he knows that people will ask about the relationship between author and character, journalist and novelist, because his last book, The People's Act Of Love, was subject to such questions, despite being set among Siberian cannibals and castrates in 1919.

"For The People's Act Of Love I had to find my inner cannibal and my inner castrate to make the writing work. In this case, it's true that I didn't have to go as far to find my inner journalist, but there was a similar process of taking the messy edges of memory and pinning them down with the crude tools of words. It's difficult to write about a character whose biography is coincident with your own, and particularly difficult to write about a journalist, because journalists are fundamentally unsympathetic characters. But as I wrote it, I felt Kellas separating from me and, at a certain point, he wasn't me any more."

We Are Now Beginning Our Descent starts with an American attack on an Iranian nuclear power station. US troops open fire on the surrounding civilian population from trucks and helicopters, shouting obscenities and machine-gunning schoolgirls in Islamic dress. It is a loud, emotive, vulgar and unreal piece of writing which suggests for three pages that Meek has abandoned literary fiction since The People's Act Of Love was long-listed for the Man Booker Prize in 2005, and taken a complete break from his past standards as a reporter and author.

"Did your heart sink?" Meek asks. He is a serious man, but also a seasoned ironist. As it turns out, the opening passage belongs to a novel within the novel, a thriller being hand-written by Kellas while working as a foreign correspondent in Afghanistan. "I'll be interested to see the reaction to that sequence," he says. "A friend of mine told me he would like to have read Kellas's novel, which amused and horrified me. But, in a way, I'd like to read it myself. I should say that one of the sources for We Are Now Beginning Our Descent was the fact that I had been thinking about actually writing that book. A Tom Clancy-style thriller, which would be redeemed in the eyes of my friends by the fact that America - Americans - were the villains. And not just villains, but dull, boring people with no sense of humour, which would be even more offensive to the American sensibility."

That thought occurred to him "at a particularly low moment, six or seven years ago", around the time that Meek was himself reporting from Afghanistan. Born in London, raised in Dundee, and originally based in Edinburgh, he had covered the first gulf war for The Scotsman and taken a posting with The Guardian in Russia for most of the 1990s, where he saw the Chechen capital Grozny destroyed before his eyes.

His first two novels, McFarlane Boils The Sea and Drivetime, had been printed to no great acclaim or sales in 1989 and 1995, and early sample chapters from his third - a peculiar geopolitical romance which refused to recognise any distinction between Russian and English literary traditions - had not yet impressed agents or publishers. Before Canongate bought The People's Act Of Love, paying him enough finally to give up his 20-year day job in journalism (although he says he will "keep his hand in", as a means of "getting out and meeting the world"), Meek considered simplifying his experiences of war for the sake of an action bestseller. "A lot of literary fiction writers assume that if they lowered themselves into the mass market, they could make lots of money. I'm not sure it's that easy, and even if I had tried, I'm not sure it would have worked out."

Instead, he has written a book that asks if war, or love, or the world, can ever be accurately reported. Kellas's American publishers are offended by the hyperbole of his fiction, while his newspaper editors prefer the decisiveness of so-called experts to the "nuanced inconclusiveness" of his front-line dispatches, and his elusive, armed and alcoholic lover Astrid accuses him of trying to slip "beauty" into reportage, where it does not belong. Meek himself has tried something similar in the past, and found that readers were generally receptive. "That said, if it seems to anyone that I have some complaint about the way newspapers report on foreign stories, that is nothing compared to my despair at the way readers deal with those stories. I think that's where the real problem lies."

The title refers, he says, "to that moment when you're travelling by air, and you can imagine that the world is as safe and pretty as it looks from a distance. It's about the perception of one country by another, because often you don't know anything about what it's like down there. That's the relationship, for example, that most British people have with Iraq and Afghanistan. Whether you are someone who thinks that the war is necessary and right, or you think everything will be fine if we just pull out, you aren't engaging, you're fantasising. It's not real life, it's just a flyover.

"I suppose I'm also thinking about the relationships between men and women, when they first get to know each other. They know there will be difficult times ahead if they proceed - they will find out each other's complications, bad habits, grisly financial details, the dark places in their psyche. But before that landing comes, they may have many serene hours of flying over a beautiful landscape."

We Are Now Beginning Our Descent is a novel without any geographical centre, as Kellas follows Astrid from Afghanistan to rural Virginia via London, New York and the Scottish Borders, pursuing old-fashioned folly by means of modern transport and communications networks. Like The People's Act Of Love, it seems literally to come from nowhere.

"There is no here' and there'," says Meek, paraphrasing Gertrude Stein. "Everywhere is here. Everyone is in touch. The only distance now is psychological." In shifting his perspective from ground-level details to high-altitude abstracts and back down again, he finds the words for this worldview. Take another scene from the war in Afghanistan: "The generators were down," writes Meek, "and all he could see of her to begin with was her silhouette against the stars To Kellas it seemed that he and the other foreigners spread out among the bushes and trees, murmuring into their satellite phones, were sitting on the edge of the cosmos, listening to the roar of time."

We Are Now Beginning Our Descent will be published by Canongate on February 7, £16.99