We were like cats but we saw no butterflies. Mostly we went on the roofs after dark. In daylight you had the view, north London laid out below you, Hampstead Heath and Highgate Wood, the heights of Mill Hill, the canal coming out of its tunnels and entering Regent’s Park, but by day you might be seen. Not everyone is in her car or stares at the ground when she walks. Once or twice we were seen but nothing came of it. What would you think if you saw three people in blue jeans and dark sweaters up on the roof of mansion flats? That they were workmen putting up an antenna, of course, or doing repairs to the guttering.

By night the lights were strung out and spread and scattered below us. No unpolluted sky was ever so starry. But up where we were, above the lights, the darkness was like thin smoke, the clouds and clear spaces above us stained plum-colored. When I first began I carried a flashlight and Liv had the inevitable candle until Wim stopped her. We must learn to see in the dark, he said, as he did. He was our teacher, as it might be a ski instructor with a class of novices on the slopes.

At my school, on the last day of term, the fourth form traditionally played a game called “round and round the room.” You had to circle the gym from the main entrance and back without once touching the floor, and you did it by means of wall bars, a horse, a climbing frame and, of course, ropes. People who inadvertently tapped the floor with a toe were disqualified. The winner was the girl or boy to do it in the shortest time. I won it easily in my fourth-form year and got the prize, a tiny silver (silver plate) cat, but unfortunately, you can’t take A-levels in negotiating gyms. The roofs of Maida Vale became my gym and a lot of other things besides. For a little while.

People would think you mad, or at least very eccentric, if you told them you climbed on roofs. Of course, you seldom do tell anyone because you know what the reaction will be. They don’t understand. They want to know why. But you might as well ask why some shoot up heroin or drink brandy or go dancing or climb mountains or do white-water rafting. They like it or they thought they would like it when they began.