A lifetime at sea is etched into a hundred faces (at least) in Chris Riddell’s Pirate Diary, the winner of this year’s Kate Greenaway Medal. Creating the cast of pirates and regular seafarers - with goodies and baddies on both sides - was a joy for the artist who has a parallel career as a political cartoonist (he’s in the Observer every Sunday, contributes to the New Statesman and does covers for the Literary Review).

Pirate Diary is the follow-up to Castle Diary, which was shortlisted for the TES Junior Information Book Award in 1999. Both books have texts by Richard Platt and both conjure up a rigidly hierarchical mini-universe (a medieval castle in the first; in the second the “Greyhound”, which sets sail from Charleston in 1716 with nine-year-old narrator Jake Carpenter on board). Both worlds are teeming with life - humans, rats and fleas packed cheek by jowl. Riddell’s illustrations of the melee at sea, based on the intricate line drawings that are his trademark, capture every rat’s whisker, every splinter in the battered planks, the worms in the ship’s biscuits and the fraying threads of the trouser legs. No wonder Pirate Diary represents more than a year’s work by one of the speediest pens in publishing.

The big picture is there too, in Jake’s dizzying view of his “world of wood and water”, the awe-inspiring glimpses of whales and far horizons and the bleak island where the cruel captain and second mate are marooned, but the stars of the show are the shipmates. “I loved drawing the figures, although there were times when whatever I did, they all looked closely related,” says Riddell. Creating Jack, his shipmates, the pirates and the Spanish crew they ambush were his reward after finishing his biggest challenge, the double-page cross-section of the “Greyhound”. “I came away feeling as if I had built that ship out of matchsticks, full of renewed admiration for Stephen Biesty (the master of cross-section illustration). But I grew up reading Look and Learn, so it took me back to my roots. The beauty of Richard’s text is that the information goes in seamlessly but it’s all there, and he leaves me room to put in the subtext; the emotional reactions.”

The same concern for historical accuracy that informed Castle Diary, his first major non-fiction project, meant his initial Treasure Island-style pirates had to walk the plank. “My first sketches had earrings, eyepatches and wooden legs; Richard pointed out that these were 19th-century inventions so they had to go. Everything was stripped away until the pirates looked as if they had been dressed by Nicole Farhi. I had to take in research at every stage so the shape of the heels and the length of the stockings belong to 1716 and not a few years later.”

His respect for line drawing (“there should be a separate award for it”) came from his art teacher at Archbishop Tenison’s school in the London borough of Lambeth. Jack Johnson was a painter who had worked on the Daily Sketch and the News Chronicle as a cartoonist. “He taught me to draw, although I had always done it at home and saw it as a treat, a way of relaxing. It’s still a treat: I’d draw even if no one was paying.”

He illustrated his first book (The Book of Giants, in Walker Books’ first series for Sainsbury’s) while still at Brighton College of Art, where he was taught by Raymond Briggs. More than 100 books have followed, most famously Something Else with Kathryn Cave, published in 1994, winner of the Unesco Prize, and The Edge Chronicles, the series of fantasy novels for upper primary readers and above that he has created with author Paul Stewart. Half a million copies have been sold, and he has just delivered book five. His solo titles include The Trouble With Elephants, The Wish Factory and, most recently, the Platypus picture books in a series for early readers about an inquisitive, energetic creature based on Jack, the youngest of his three children. He likes to work across a wide age range, and has a perfect long-term project for older readers in Gulliver’s Travels, which he is illustrating for Walker. The artwork combines his two skills, political caricature and fantasy. “Swift was reflecting his world of palm-greasing and jostling for preferment through other worlds in which you can make up anything you want. I’m having great fun with it.”