I can write best in this room by pretending to myself that it's a tree-house. It looks quite normal in this photo, but what you can't see is either the quantity of wood or the view, which makes this ongoing fit of delusion possible. Because it's built so high above gardens, with an uncontrolled tangle of jasmine at the window and much creaking of floorboards, it's quite easy to imagine I'm in a wooden hut swaying among the trees and conveniently fitted with bookshelves. I dream of a real treehouse study, but the one spindly, woody specimen in the garden can barely support a bird-feeder, let alone the Swiss Family Robinson cabin of my imagination.

I'm in the last weeks of writing a novel set on Dartmoor, so my mind is full of rivers and racing clouds. Above the desk is a precious birthday present, Dartmoor by Arthur L Salmon, published in 1913, with fog-laden colour plates. The desk was given to me by my father when I was young and wanted to become "an authoress". The chair was nicked from an office I used to rent for 20 quid a week in a building that resembled a public lavatory. It was the only chair I ever found that didn't induce instant scoliosis so when I gave up the office after a section of ceiling crashed on to my desk, I brazenly walked out with it, and carted in an equally ugly replacement.

The children's art is around to remind myself of them in the day, and on the left wall I keep a photo framed by my publishers of the tube campaign for my last novel. I often take my laptop to cafés or the British Library to escape the internet. It's lucky I can write anywhere: my beloved wooden study is threatened with becoming a bedroom.