The concourse wasn’t too bad, but when I got to the Oxaloo Line platform I found it so packed that I thought I would never get on the train, and the closeness of the coughing bodies and lack of air made my head worse. As the carriages came to a halt, we all shoved in, staring straight ahead, not speaking to each other, and I only just managed to get on. While we shuffled around, my eyes fell on a poster above the seats, warning of the threat of infiltration, showing tunnels burrowing from the DUK land – everything north of a line stretching from Bristol to Norfolk, plus the north-western quarter of London – into our Republic of Great Britain, covering southern England and the rest of the capital. Constant vigilance was needed, it said. Then a man pushed in front of me, blocking my view of the poster.

The train started up and rattled away from the now-deserted platform. They say that during the Blitz, the men and women who used the Underground as a shelter at night would just take themselves off to quiet corners without even knowing each other’s names. No doubt, thinking you might get blown apart as soon as you set foot above ground makes you realize that there are some things you don’t want to go to your grave never having tried. And I think it was seen as patriotic too if it were some young man being sent to the front who might never come back – to give him something to smile about when he was on the ship going over.

Not many did come back, of course, and I knew some of those who didn’t: boys I had grown up with and would never see again except in my mind’s eye. I had held those sickness-inducing photographs of the D-Day beaches, though – countless bodies with their heads or limbs missing. Tens of thousands of corpses floating in the water. The Germans had taken a lot of images to celebrate how victorious they had been over us. Then, after the Red Army had, in their turn, defeated the Germans, we had been shown those images to learn how lucky we had been that the Soviets had come to our aid. Either way, the photographs had left me feeling ill for a very long time.

After forcing my way out at Waterloo, I passed the broken remains of Westminster Bridge that invited you to step off the bricks and into the river. That’s if you could somehow scale the electrified wire and stay hidden from the guard towers and their searchlights, of course. Everyone had heard of someone who had managed it, but the stories were always second-hand, and there was a line of simple white crosses on the other side for those who had slipped silently into the black water at night and tried without success.