Six years ago, I won a commission to photograph eight British cathedrals for the Royal Mail. Subsequently, with English Cathedrals by Edwin Smith and Olive Cook as my guide, and a pack of "Anglican Cathedrals of England" Top Trumps, I set out to photograph all 42.

I began by photographing the aesthetic highlights of each building, but the images seemed to merge into one another. In order to differentiate each place, I needed to find a more rigorous and systematic approach, and so I adopted the simple strategy of photographing the naves, looking along the central axis.

There were other decisions to be made: whether to photograph from the east or west, for example. I always tried both, and often entered during darkness, setting up my equipment in front of the west door, and waiting for the sun to come up behind the altar. The viewpoint added depth to the visual experience of the building, and the discipline of this strict approach was liberating, as I simply looked, allowing the power of the place to unfold in the dark.

The sense of mystery was absent, however. I found it by accident at Rochester, just before dawn. When I entered, the lights were all turned off, and the huge, silent space seemed locked in time, as if it were there just for me. In the half darkness, the very air was tangible. I knew then that this was what I needed to discover in all the cathedrals.

It was not easy to arrange to have the lights turned off, but I soon realised that it was essential, allowing the buildings to come quietly to life in the tentative morning light. When the lights finally went back on, as services began and visitors and school groups started to arrive, the magic evaporated at the click of a switch.

The photographs are in the PDF or paper versions of the Church Times on page 20. Identify as many as you can. Answers on page 30.

These photographs can be seen at the Wapping Project Bankside gallery, 65a Hopton Street, London SE1 9LR. For more details phone 020 7981 9851, or visit the website thewappingprojectbankside.com.

The photographs also appear in The English Cathedral by Peter Marlow, published by Merrell at £45 (Church Times Bookshop price £40.50 ).