"The reason why so many of my photographs in the book were taken in stairwells and corridors was that that was the only bit of spare space available and, in some cases, the only place where there was enough light to see anything. Even then, it was often so dark that I couldn't tell which gender my subject was (not that I particularly cared) and too dark, before the era of autofocus, to focus. I had to find a light (or carry a torch) and pre-focus."