Some writers claim to extrude a book at an even rate like toothpaste from a tube, or to build a story like a wall, so many feet per day. They sit at their desk and knock off their word quota, then frisk into their leisured evening, preening themselves.

This is so alien to me that it might be another trade entirely. Writing lectures or reviews – any kind of non-fiction – seems to me a job like any job: allocate your time, marshall your resources, just get on with it. But fiction makes me the servant of a process that has no clear beginning and end or method of measuring achievement. I don’t write in sequence. I may have a dozen versions of a single scene. I might spend a week threading an image through a story, but moving the narrative not an inch. A book grows according to a subtle and deep-laid plan. At the end, I see what the plan was.

I used to be a late starter, but now I get up in the dark like a medieval monk, commit unmediated scribble to a notebook, and go back to bed about six, hoping to sleep for another two hours and to wake slowly and in silence. Random noise, voices in other rooms, get me off to a savage, disorderly start, but if I am left in peace to reach for a pen, I feel through my fingertips what sort of day it is. Days of easy flow generate thousands of words across half a dozen projects – and perhaps new projects. Flow is like a mad party – it goes on till all hours and somebody must clear up afterwards. Stop-start days are not always shorter, are self-conscious and anxiety-ridden, and later turn out to have been productive and useful. I judge in retrospect. On flow days, I have no idea what I’ve written till I read it back. It’s a life with shocks built in.

I don’t mind whether I write by hand or on a keyboard. I don’t mind anything, as long as I’ve woken up calmly in my own time. I’m a long thinker and a fast writer, so most days I don’t spend much time at my desk. I concentrate well. I’m not tempted by the internet. If I’m redrafting, fine-tuning, I print the text and take it away to read it on paper. But if I’m writing straight on to the screen, I tense up till my body locks into a struggling knot. I have to go and stand in a hot shower to unfreeze. I also stand in the shower if I get stuck. I am the cleanest person I know.

I am fuelled by tea. I don’t want to break to eat. But after an intense bout of work I might fall asleep, which gets me fit for the next bout. I stop for the day when some inner falling-away says, that’s all there is. It feels like a page turning inside – the next page is empty. Nothing is left then but to go to bed and wait for dreams and for the next day.

About half my working year is like this. The rest involves talking, travelling, producing a public persona – but still with odd hours, and a constant output of ideas. The most frequent question writers are asked is some variant on, “Do you write every day, or do you just wait for inspiration to strike?” I want to snarl, “Of course I write every day, what do you think I am, some kind of hobbyist?” But I understand the question is really about the central mystery – what is inspiration? Eternal vigilance, in my opinion. Being on the watch for your material, day or night, asleep or awake.