Terry Pratchett: "Writing for children is more a matter of tone rather than whether it's got drug references"

There is an undoubted suggestion of the cat who got the cream about Terry Pratchett when I meet him in a hotel room in west London. He is, I would say, feeling just the teensiest bit smug – as most of us would if we sold as many books as he does, and had just won the Carnegie Medal for an outstanding book for children.

The pleasure is enhanced by his genuine surprise at winning. For two reasons: one is that, having been shortlisted twice before, he made a point of not assuming he would win. But he's also surprised because he didn't think that The Amazing Maurice and his Educated Rodents (Doubleday, £12.99) was the sort of book that won prizes. "In recent years the Carnegie has had a reputation for, shall we say, going to 'gritty' books, with a few 'social issues' involved," he says. Since Maurice is a) a fantasy and b) very funny, it was, he thought, excluded from winning more or less by definition.

In fact, Maurice is, as the Carnegie judges recognised, a deeply serious book. The rodents of the title are rats, and they are not educated as such, just very, very intelligent – the result, we gather, of eating magical detritus on a rubbish tip outside a wizards' university. This also accounts for their somewhat surprising names – Darktan, Sardines, Nourishing, Dangerous Beans – scavenged off cans and boxes on the tip, before the rats could properly understand what the words meant.

Maurice is a cat whose mind has also been expanded in unexpected ways, though in his case the reasons are somewhat mysterious given that he doesn't eat rubbish (the explanation is a crux of the book). Unlike the sociable, somewhat idealistic rats, Maurice is a cynic and an egotist ("Bilko in fur," Pratchett suggests): a cat determined to get his paws on the cream, or at any rate the cash to buy it. He has dreamed up the scam that keeps him and the rats. The rats go into a town and plague the populace more effectively than ordinary, dumb rats ever could; then along comes the magic piper – actually Keith, a "stupid-looking kid" recruited by Maurice, who plays his pipes, dances the rats out of town, and collects his fee.

This would be enough plot to keep many novelists going; but Pratchett is a prodigious creator of narratives, and this is only the back-story, painted in swiftly. The main plot describes what happens when Maurice and the rats, arriving at the town of Bad Blintz, run up against a different intelligence: a Rat King, a composite mind created when several rats have their tails knotted together. Maurice's rats dream of a world where human and rat live in harmony; the Rat King wants to fight humans for mastery of the world.

Although Maurice is not gritty in the sense of dealing with the quotidian social issues that abound at the more serious end of children's fiction – drugs, race, finding out you're gay – it is packed with powerful themes and images. The most impressive moment comes when the educated rodents enter a cellar where thousands of starving rats have been caged, and their newly found intelligence is simply swept away by the atmosphere of fear and hatred that washes over them. Once again, they are merely "vermin". The echoes of Nazi genocide are never overtly stated, but inescapable; yet despite the context of fantasy, it doesn't seem tasteless in the way that Martin Amis's self-consciously serious Time's Arrow did.

There are other intriguing strands: the reader sees the rats develop a capacity for symbolic thought, along with a slowly deepening morality, a sense of kinship with other creatures who have brains, and compassion for those who don't. They begin to become afraid of the dark – a good thing, says Dangerous Beans, their sage, because it shows they have begun to distinguish between the darkness outside and inside.

A sub-plot revolves around Malicia, daughter of Bad Blintz's mayor, who believes that life works like fairy stories. The press release for the Carnegie Medal praises Maurice for highlighting "the danger of allowing stories or fantasy to replace reality"; in fact, it is subtler than that. What Malicia learns is that, quite a lot of the time, life does fit into the pattern set by stories. Even if it doesn't, she can sometimes shoehorn it in.

In America, the world of children's books is dominated by what Pratchett calls – with, he insists, some affection – the "dirndl mafia": a coalition of teachers, librarians and reviewers who take an earnest, improving view of literature. When Maurice was published there, it was treated with great seriousness and attention to detail. Over here, though, he still gets pigeonholed, and it riles him: "Many of the reviewers in the newspapers went 'Oh, a wacky, zany book by best-selling Discworld author Terry Pratchett,' when in fact Maurice has very little wack and hardly any zane."

He mentions one newspaper article which said, roughly, that the Discworld books sell in huge quantities because they are bought by 14-year-old boys called Kevin: "In fact, as far as we know, 60 per cent of my readers are female, over the age of 25 – don't ask me, a lady actually did a survey."

It is true, though, that the Discworld books get an awful lot of young readers: something that occasionally worries him a little, as when a group of schoolchildren wrote to him about The Truth, a Discworld novel in which one character is obsessed with ingesting white powder. He comforts himself with the thought that "there's nothing in it that they don't know about from the playground". It's also the case that his adult fans snap up his children's output (which apart from Maurice comprises two trilogies: Truckers, Diggers and Wings; and Only You Can Save the World, Johnny and the Dead and Johnny and the Bomb).

I wonder what Pratchett sees as the difference between writing for children and writing for adults. He mentions the difficulty of not having a common frame of reference – will children understand an allusion to the Fab Four? However, "that's almost just a technical issue".

Other than that, he doesn't think the content is the important thing: "Writing for children is more a matter of tone and approach than language, how the story works rather than whether it's got drug references." He pauses, then expands: "It's still allowed to be a children's book, even if it's got no drug references in it."

"One thing that I am aware of with Maurice: you say to the kids, 'The rats are intelligent because they ate a lot of old magical rubbish that had been chucked over the wall of a magical university,' and the kids say, 'Fine, let's get on with the story. We're quite prepared to accept any amount of garbage like that if we then get on to a good story.' The adults say, 'Hang on a minute, how did this make them intelligent, as opposed to green?'"

There is one other thing that distinguishes Pratchett's children's books: scale. They tend to be more compact, or at least more tightly plotted and written, than the Discworld titles, which start out enjoyably but usually go on about 100 pages too long, for my taste. For another, the children's books tend to be about miniature worlds. The rats in Maurice, the four-inch-high "nomes" who are the heroes of the Truckers trilogy: both are small creatures living on the margins of the big people's world, imperfectly understanding its manoeuvrings. Is the idea that children are supposed to identify with that?

"Children and very small creatures have things in common," Pratchett agrees. More to the point: "A quick way of getting a different perspective is to change the size of the person who's doing the looking."

He cites G K Chesterton's view of fantasy: the idea is "to take that which is familiar and everyday and therefore no more seen, and pick it up and turn it around and show it to the reader from a new point of view, so that once again they see it for the first time". That's what Pratchett has done in his best books, and The Amazing Maurice is one of those: a very grown-up story, and a deserving Carnegie winner. E

Terry Pratchett: Biography

Terry Pratchett was born in 1948 in High Wycombe. He left school at 17 to work in local newspapers; in the Eighties he was a press officer for the Central Electricity Generating Board, specialising in nuclear power stations. His first novel, The Carpet People, was published in 1971; in 1983 he published The Colour of Magic, his first book set on the Discworld, a flat world which sits on the back of four elephants which stand on the back of a giant turtle swimming through space. He has now written 25 Discworld books: each sells more than 150,000 in hardback and 350,000 in paperback in this country alone. His total sales now exceed 27 million copies. He regularly heads both paperback and hardback bestseller lists, and is the only author to have topped adult and children?s lists simultaneously. He writes two books a year, and in the Nineties was Britain?s best-selling author. His awards include an OBE for services to literature in 1998. He is married, with one grown-up daughter, and lives in Wiltshire.