I do always know where I'm going in my books. I know the endpoint. I've written only two thousand words of my next novel but I know what the ending will be already.

We have this sense that there's something bigger than us, above and beyond. If you take away the idea of God, you need to replace it with a shared moral code. Otherwise, everybody becomes very self-centred and materialistic.

There are very good evolutionary reasons for having religion. From early human history we have evolved a need to see God. We have a perception of ourselves and in order for that to be a true perception we have to believe in a soul within us.

I wanted to write a book that imagined where advances in the study of genetics might lead us. Holman was the first character who came to me: I envisaged the misshapen offspring of beautiful, wealthy parents. Then I realised that he bore a striking resemblance to Toulouse-Lautrec. I developed that, made Holman an alcoholic who lives among hookers, an artist tortured by his disability.

I debated whether or not to pin the setting down to a particular date but in the end I decided to leave things vague. It depends how fast technology improves.

What I imagined doesn't require anti-gravity beams or anything too spectacular, just advances in analysing different genes, finding out what they can do and recombining them.

I'm a hardened atheist but I feel that we have an inbuilt need for God. If you eradicate religion, you end up with something terrible in its place, like the communist state, as in Russia or China, where the dictator becomes the messiah figure.