How did Twinkle, Twinkle, Little Shark! come about?

Well, I like making up silly rhymes and parodies, and one day, when my sons were about 4 and 7 years old, I found myself muttering to myself "Twinkle, twinkle little shark". My next thought was "Who would say 'Twinkle, twinkle' to a shark, and why?" The obvious answer was somebody singing a lullaby to a sleepy shark, and that led to the second line and the rhyme "Don't be frightened of the dark."

I then came up with the idea of animals getting ready for bed, and my elder son Thomas contributed some ideas such as the bear and the snake, but it was a while before I worked out exactly who was putting the animals to bed and why! I drew the illustrations and added the text at the same time.

It was only once I had printed and put together a mock-up of the book that I realised that the verses could be put into an order that made sense in terms of a child getting ready for bed!

It's significant that none of the animals in the last picture have "accessories" - no teddy-bear, hot-water bottle or toothbrush. Imagination is the key to the story.

Tell us about the style of your illustrations. What are some of your influences?

I have always preferred using sharp-edged blocks of solid colour without outlines. I first discovered this style when I did silk-screen printing during my last years at school, and later in life applied it successfully to logo design for companies. I love the work of Julian Opie, Henri Matisse and the Op and Pop artists of the 1960s.

Sometimes I use photos either as references or to trace. I always simplify them, often straightening out perspective or reducing shading to solid areas of colour. My main graphics tool is XaraXtreme Pro, a program which is similar to Adobe Illustrator but which I find much easier to use. I do all my drawing with a mouse - I have never got used to graphics tablets, and I never use auto-tracing facilities. It's all done by hand.

The characters in my books tend to be animals. They are drawn freehand and then tweaked to make them less lumpy. I liked the effect of the silhouetted characters in Twinkle, Twinkle, Little Shark! so I decided to continue using that. The main character in Bob is the first to be a realistic colour, but even so he is still a solid orange shape and never moves from one picture to the next!

My animal characters have eyes with expressive pupils, but rarely a visible mouth. This is very important to me. I got the idea from E.H. Shepard's illustrations for Winnie-the-Pooh. Pooh Bear is rarely depicted as having a mouth, and it gives him an air of inscrutable wisdom - he knows everything but (as a real-life toy) can express nothing. When Disney Americanised the Bear, they gave him a sarcastic smirk - I really don't think they understood.

Where did Armadillo originate?

My younger son, William's favourite animal is the armadillo - he probably got that from Twinkle, Twinkle. I had made up a little jingle to the tune of Clementine that went "Armadillo, armadillo, armadillo, so are you / Armadillo, armadillo, armadillo, you're one too!" This was unsatisfactory as it made no sense, so I started singing "Armadillo, armadillo, armadillo in Peru / Armadillo, armadillo, la la la, la, London Zoo". Eventually I worked out that the armadillo "wants to visit London Zoo", and the story evolved from there, including the reason for the journey.

I felt a bit guilty that the child in Twinkle, Twinkle was definitely male - why potentially alienate half your readership? - so I deliberately made the gender of all the characters in Armadillo non-specific. It makes it a little more difficult to write the verses because you can't just say "he", "she", "his" or "hers" without thinking! It helps the reader to identify with the character; to a girl the armadillo might be female, while to a boy it might be male. Or vice versa. Again, imagination is the important thing.

How about the backgrounds in Armadillo?

I had initially considered a completely different style - maybe pencil drawings with lots of detail and shading. But I liked the silhouette idea that I had used in Twinkle, Twinkle, and I thought it might work with colourful backgrounds. Scenes like the Peruvian hillside and the view of Rio were hand-traced and simplified from photos; London Zoo, Lima Airport and Southampton Central Station were drawn using photographic references; the ship in Rio was traced from a 3D model of MV Adonia, a cruise ship that really does sail from Rio to Southampton! The pictures of the ship at sea and nearing land are based on a still from a video of Adonia approaching the Southampton docks. The rain-forest scene and the London Tube station were drawn from my imagination.

Bob seems to mark a return to the simplicity of Twinkle, Twinkle…

Yes and no. The premise is a simple one. Bob is the best goldfish in the world. That's something that a child might say about his or her pet. No justification needed. A goldfish doesn't have to do anything to be loved, but a child may feel the need to do something for their pet.

The plot itself is quite abstract. Bob may or not actually be bored with his surroundings (apart from his pupil, he doesn't actually move throughout the book), but the child's love for the fish drives the story. Concern for the fish becomes a flight of fancy, from the everyday ("can you get wallpaper for goldfish?") to famous landmarks, the wonders of outer space and a cave full of treasure before reality kicks in, but any possibility of disappointment is prevented by the promise of a happy pet.