I guess I am never going to write an anti-hero, but what I like doing is taking a character and making them seem comical or cowardly or silly, and then producing a paradigm shift so that we can see that all of these things can hide incredible courage, depth and blinding beauty of spirit. I always suspect it of my characters, and when it comes I am always shocked and touched by it. I guess that is the thing I love most about writing: the moment when a character I have created reveals the bit of itself that I did not invent or expect. The bit where they take on their own life …

The last instalment of the Obernewtyn series, The Red Queen, isn’t far from being released. How difficult is it to close a series that’s been with you for so long?

It’s further away than my fans or publisher likes. It was supposed to come out this year but I found I just could not work when the book was scheduled and everyone was hanging on me finishing. It was like trying to work in a room where people were shouting at you that you were going to miss the bus. Luckily, Penguin have been able to bear with me and the final book will be coming out next year.

I know some writers can deliver a book exactly when they say they will, but I honestly don’t know how they do it. For me a book is a journey and I don’t know how long it will take. I have a map, but it is sparse and there are so many things to see and learn and explore before I find what I set out to find. I write in order to think and that means I don’t know how long it will take me to figure it out. I think of it as a very organic process but that might be a nice way of saying ‘utterly disorganised’.

Despite the size of the books, I really have to work to fit everything into each one and I cut and cut and cut to do it. It’s hard work but incredibly satisfying, and it is balanced with elaborating and clarifying, because the stories are all very complex. For me the process of editing does not happen after the book is finished but is part of the whole creative process. Finishing will be a wrench in the same way that finishing Phillip Pullman’s His Dark Materials books were a wrench for me, as a reader, or the Narnia books when I was a kid … or Steig Larssen’s Millenium Trilogy. But they must be finished and that is that. And I want to finish them. I want to come to the end of it because I want to know exactly how it will all come out as well. But unlike readers, when I have finished, I will never ever be able to go back through the wardrobe door again. At least, not that door …