Sitting in a booth at Edinburgh's Christmas Spiegeltent on Festival Square, Nick Sharratt is getting a quick preview of the show he's come to the city to see. You Choose is the adaptation of his and Pippa Goodhart's own multiple choice storybook, his most successful of a batch of roughly 250, including works with best-selling authors including Jacqueline Wilson, Julia Donaldson and Giles Andreae. In the background, actors Paul Beeson and Carrie Mancini are doing tech for that morning's performance of Scottish company Nonsense Room's new production.

'I'm really looking forward to it,' says Sharratt, suitcase at his feet as he prepares to fly back to his home in Brighton after he's seen the show. With a beard, colourful shirt and tanktop, and a friendly smile, he has the look of an old-fashioned television presenter about him. 'Nonsense Room have already done the Shark in the Park books, a very wonderful play combining my three short stories, and I was very impressed with it,' he says. 'They suggested You Choose and I'm interested to see how it goes; I remember when I was a boy, one particular theatrical experience was an interactive, improvisational show that I went to, and that stayed with me until I came to make You Choose.'

You Choose – and its sequel Just Imagine – are children's books like no other, vivid explosions of colour and imagery which present not so much a narrative as a pick 'n' mix of situations, settings and costumes for readers to invent their own scenario with; which Nonsense Room represents in the form of audience games and participation. 'I gave a talk once to a group of authors and Pippa Goodhart was in the audience, where she saw a very detailed picture I'd done when I was a boy,' recalls Sharratt of the book's origins. 'She wondered if I'd be interested in having a go at some busier pictures and this was the result.

'She mentioned the idea that it was more like a catalogue,' he continues. 'We both had the same fond childhood memories of looking through Littlewoods catalogues and going into this wonderful dream world where you can choose whatever you like. The hamper was the one I always liked, food is one of my favourite subjects. All that wonderful choice in those catalogues, and it was fantasy, you know? You couldn't really live off Christmas hampers all year round. It's bit daunting when I'm faced with an empty page, but the wonderful reception the book got has made the follow-ups really enjoyable, because I know nothing goes amiss. All that effort, every little detail, and I know somebody, somewhere will pick up every little thing.'

His deceptively simple, beautifully coloured pictures are drawn by hand and coloured digitally. Sharratt says he wanted to be an artist from around the age of nine, and he studied at art college and originally went into magazine illustration. 'I've always drawn in pretty much the same style as I do now, with a black line and really bright colours. I grew up in the 1970s, so I was influenced by the aesthetic of the time and I never really lost that. I haven't grown up beyond the age of primary school, and I think my colour palette, the way that I draw and my sense of humour seem to strike a chord with children; I have an approachable style that they aren't intimidated by. Picture books is a really lovely area to be in, it gives you a lot of creative freedom and you can really stretch your imagination. I don't have kids of my own, so I rely on my own clear memories of what it's like to be a child and what appealed to me.'

The versatility of Sharratt's style means the books he illustrates cover a wide age range, and at the moment he says he's working on a new Jacqueline Wilson story, some picture books, including those for small toddlers, and that there's a possibility of another 'instalment' of You Choose, although these books are visual research-heavy and can take up to a year to complete. 'I want my readers to be entertained and find the books fun and amusing,' he says, 'and I think that if a book is entertaining then it can have other qualities to it, it can be subversively educational and maybe teach them something new. There's nothing more rewarding than seeing a child enjoying one of your books, and I'm very happy to have found that little niche for myself.'

You Choose is at Festival Square Spiegeltent, Edinburgh, until Sat 5 Jan.