Stephen Biesty has been drawing castles, and what goes on inside them, all his life. What began as a boyhood passion - drawing scenes from history, Vikings, knights in armour, Roman soldiers in battle - is now his livelihood: he is the best-selling illustrator of pictorial reference books, including Incredible Cross-Sections, Cross-Sections Castle and Cross-Sections Man-of-War.

It was always the visual aspect of history that excited Stephen Biesty. Not a bookish child, he was inspired more by the historical epics he watched on television - such as Spartacus and Ben-Hur - than by what he learned in school. “I was not interested in history in an academic way, but I had an instinctive response to atmosphere, to the feeling you get when you walk into a castle ruin, that sense of the past.”

Encouraged by his father, a coach painter with Rolls, to pursue his drawing professionally, after leaving school in 1979 he took a first-class degree in graphic design at Brighton Polytechnic, specialising in historical reconstruction illustration. He did an MA in graphic design at the City of Birmingham Polytechnic, and then began to hawk his ideas around the London publishing houses.

“To earn a living, I had to streamline my style: there wasn’t time at first to do what I really wanted to do - which was to go into a lot of detail.”

His big break came in the early Nineties, when Peter Kindersley, at Dorling Kindersley publishers, suggested he have a go at drawing cross-sections of buildings and machines. Eighteen months later, Incredible Cross-Sections, which has sold more than a million copies, was the result.

The book is a series of 18 large drawings, including castles, galleon, space shuttle, opera house and ocean liner, each one a rich blend of technical and human detail, jauntily annotated by Richard Platt, to explain how it works and what people do inside. Occasionally the detail is so tiny as to almost strain the eye; the most successful, such as the galleon, are those drawings where you can discern gesture and facial expression, giving great opportunities for colour and humour. Barely a page goes by without someone, somewhere, sitting on the loo.

Stephen Biesty’s love of detail is perhaps the key to his success, creating as it does a natural affinity with his young readers. “Children love to pore over detail - in the same way that they are fascinated by anthills, or by using a magnifying glass,” he says. “The more detail there is in my books, they tell me, the better they like it.”

Cross-Sections Castle and Cross Sections Man-of-War (now also available as a CD-Rom) quickly capitalised on the Stephen Biesty “new look”; Incredible Explosions, which takes an unusual view of history from the Big Bang, is in the pipeline for this autumn.

The achievement of all of them is that they are useful reference books which make finding out feel like fun. “I’ve heard that they are particularly popular with boys who are reluctant readers. Teachers have written to say that the books have helped get boys into the habit of going to the library, because they see it doesn’t all have to be boring stories.”

Biesty himself has no pedagogic ambitions for his books: he simply does what he likes doing, and what he does best. “I like to do things that are going to astonish. I’m glad if my books help whet children’s appetite, by being colourful and not too serious. Once children are interested in something, they make more effort - and perhaps my books help take that first step for them. ”

Stephen Biesty works from the quiet of a Somerset village, where he lives in a converted school house with his wife, Liz, and their three-year-old son, Richard. His small studio, overlooking the village church, contains neither a computer nor sophisticated drawing boards: his only equipment is A4 cartridge paper, and a few jars of watercolour brushes, propelling pencils and isograph pens.

Using plans, guidebooks and historical records to research his subject, his great gift is then to visualise it in three dimensions sliced into interesting cross-sections. Impressively, he draws almost entirely by eye, barely even using a ruler: “My father did teach me about perspective and vanishing points, but I think you have to have a feel for it.”

While extremely accurate, his drawings thus retain a hand-crafted, friendly quality which Biesty greatly values, being not too dry and not too slick.

Illustrating children’s non-fiction is an altogether smarter, brighter business than in Biesty’s own childhood. The pictures in one of his favourite boyhood books, Rulers of Britain, which he still has, are hasty, slightly crude pen-and-ink washes, which already look very dated.

“Those older books required more effort from the reader. The newer ones say much more - ‘look how interesting we are’.”

Photographs are used now more extensively and effectively than in the past (for instance, Dorling Kindersley’s EyeWitness Guides), but speaking as a craftsman, Biesty is not always in favour. “I think people like to feel the detail has been laboured over. Detail is often less apparent in a photograph, whereas a good drawing really brings it out and displays it.”

Illustrations that are too photographically accurate can be daunting for children, he says, because they cannot hope to imitate them. “With my cross-sections, when I talk to children in school, I often suggest they make one of their own house - and put dad on the loo.”