For a generation of Britons, war was the defining experience of their lives. In her Costa Book Award-winning novel, AL Kennedy looks at the moral price they paid. She talks to Stuart Jeffries.

'I can never cry when there's a guy in the room without him immediately trying to hump me," says AL Kennedy unexpectedly. A few hours earlier, the Scottish novelist had won the £25,000 (€33,560) Costa Book Award for her novel, Day, about the post-second World War psychic meltdown of the eponymous tail-gunner of a British Lancaster bomber. It's 1am at the London hotel where the award was announced, staff are clearing tables, the black ties and posh frocks have all gone home, and I'm confused. How come we're talking about Alison Louise Kennedy's sex life?

Why, I ask in bleary innocence (it's past my bedtime and I'd expected to be talking about her fifth novel's themes of war, male camaraderie, the ethics of British bombing raids over Nazi Germany, the nature of British culture and the future of the literary novel, rather than her experience of sexual harassment), does she elicit such untoward approaches from men?

"I think it's because they can't think of anything else to do," she says. When a woman cries? "Yes, it's like 'this'll cheer you up'. And I'm like: 'But I was actually telling you about a complicated, awful relationship that I'm still recovering from. Put it away. What's wrong with you?' "

How did we get on to this? I was telling Kennedy about how difficult I found it to interview novelist Julian Barnes, and she said that he had a reputation, adding: "But he was very courteous to me. Perhaps it's because I was wearing a neck collar."

Why would that help? "He obviously found that exciting. If you want to score quickly, wear a surgical collar. It's quite disturbing. It's like they can't respond to you unless you're injured. They really are, like, circling the herds of zebra, looking to pick off the gammy one. And I'm like, 'but I was looking for romance'." Men, eh? "Yeah," she agrees, grinning. "Wankers."

Kennedy sips her mineral water (she's allergic to alcohol) and looks into the middle distance.

This is the woman who told the Observer newspaper that she has lived alone since she was 17 and that she has sex about once every five years.

Previous interviewers have detected self-pity in Kennedy's narrative of her singleton lifestyle, but they seem to miss her talent for ironic overstatement. She is, after all, not just a prize-winning novelist but an accomplished stand-up comic who has plundered her own presumed glum biography, making it into comedy through exaggeration. At least, let's hope. Personally, I found her charming, though God knows what I'd have done if she'd started crying. Anyway, what she'll soon realise, thanks to her increased bankability, is that men find money even more of a turn-on than tears.

"Once I couldn't make a living purely from writing, but in the last year I seem to have won lots of prizes," she says.

She not only won £25,000 from Costa for its book award, but an additional £5,000 (€6,700) for winning the best novel category. "And the thing is, the prize money is tax-free," she adds happily. What's more, she expects sales to rise.

KENNEDY'S NOVEL WOULD take the froth off anybody's cappuccino, even the Costa judges'. It's a delightfully grim, sometimes vexingly elliptical, structurally sophisticated, occasionally stylistically clotted novel about what war does to some men; how it gives their lives meaning and how, when it ends, that meaning can disappear catastrophically.

The hero is 25-year-old Alfie Day, all 5ft 4in of him (a good size for squeezing into a Lancaster turret). It is 1949 and he is returning to the Germany that he and his Lancaster crew helped bomb to smithereens, and where he was imprisoned after his plane and his mates were shot down. He's returning to take the role of an extra in a POW film, but his aim is to find out where his life went wrong and whether he can piece something happy together from its wreckage.

Much of his story - his induction into the bomber crew, his love affair with the implausibly posh Joyce, his boyhood, his incarceration in wartime Germany - is told through a demanding flashback structure.

In Kennedy's symbolic schema, Day comes to life at night - that's when he flies, and it is during a blackout that he drowns his father, whom he believes to have murdered his beloved mother, in a canal. Significantly, Day is from the Black Country in the industrial west midlands of England. He escapes it for war's unforgiving light, to shine in a new, lusty life. "But we did so well," says a minor character towards the end of the book. "So many people did so well . . ."

In Kennedy's estimation, the British shine in war, ultimately sinking back into selfish darkness in peacetime.

It is that wartime capacity of the British that Kennedy sought to honour - as well as question - in her novel. She isn't writing a judgmental book, but rather trying to get into the heads of those men who did the bombing. Weren't their moral compasses limited?

"Out of necessity," she says. "They couldn't have done what they did if they were otherwise, or if they had the benefit of hindsight."

Why a Lancaster tail-gunner? "It's just metaphorically very interesting. You're watching everybody's back. When you bail out of a turret, you bail out backwards, you look at where you've just gone and what you've just done. In memoirs, tail-gunners talk about this giant hand coming to reach you back. Being so isolated, any kind of communication would be difficult."

It's strange that Kennedy didn't write a more hostile novel, given her politics and the research she did.

"I started writing this when I was completely hemmed in writing anti-war stuff before the whole Iraq thing blew up," she says. "Then day after day after day of bombing Afghanistan and bombing rocks into gravel and gravel into sand. I started just looking at all the aerial-bombing arguments and realised we should have learned from what we did wrong in the second World War."

Instead, "we went back to sleep," argues Kennedy, believing "that we were always good. We weren't".

I tell Kennedy that my parents hailed from Wednesbury, the Black Country town from which Day escapes into the thrill of war, a place whose heavy industries the Luftwaffe tried to but couldn't quite finish off (British Conservative governments were more thorough), while the RAF was bent on reducing German cities to simulacra of the fires of hell. Why did she choose a Black Country boy as a hero?

"I knew about it because my grandparents were from there," she says. "It's an industrial area where people did very dangerous jobs and could be killed at any time, and extreme levels of poverty."

She was drawn, too, to the strange dialect. "There's an enormous sense of humour in the way Black Country people speak. It's a very playful and very old language."

Research for the novel was not done in the Black Country but in the reading room of London's Imperial War Museum and in the Lincolnshire Aviation Heritage Centre in eastern England.

"I've long been interested in that period," Kennedy says. "It started, I guess, when I was beginning to write, and working as a community arts worker, and spending a fair amount of that time with people of that generation in occasionally terrifying hospitals, and just saw these astonishing men who had had everything asked of them and who'd given everything and who'd given me a public transport system and a national health service and an education system and a Britain that at least tries to value everybody. Because they found out that was true - that they had to value everybody during the war, and there was a kind of meritocracy afterwards."

What does a writer born in 1965 have to tell us about that wartime experience? "It was just very hard hearing stories from people when you didn't know if you could face what they faced. And there they are, sitting in their own urine, eating stew that smells like urine. Not all of them, obviously, but I felt a debt and I always wanted to write about that generation."

IN HER ACCEPTANCE speech, Kennedy spoke of the importance of literary fiction in British culture at a time when much that is cherishable about that culture is being destroyed.

"We are trying to disassemble our culture," she said, and then reached for martial imagery. "And normally only an occupying force would do that."

What did she mean? "I've been reading about Raphael Lemkin [the Polish- Jewish lawyer who in 1944 sought to define the term "genocide" and whose work led to the UN's Convention on the Prevention and Punishment of the Crime of Genocide]. He talked about the precursors to genocide, which are about preventing a population from expressing itself and from having an imagination, preventing a population from seeing themselves as human, redefining themselves as things. Coming across that was important for me. Then you look at the average day on British television - one big reality show of fat, stupid, thieving, selfish, ugly people. If you get that daily, it is going to start changing the way you feel . . .

"Fiction is participative. When you get into it, it's about you exercising your imagination. And if you can no longer exercise your imagination because it has atrophied, you have reality television and books about multiply abused amputees, because it's great to stare at them because they're animals and your life is so miserable that you really need programmes about people who are excessively miserable to make you feel better.

"But use of the imagination means that you can make your life or someone else's life better and that they're humans with interior lives and not just somebody on the EastEnders soap opera going 'you stupid cow'. It means you have the imagination to change the government, to know when you're being lied to."

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