Teargas is awful – it gets you in the back of your throat and burns your eyes. It drifts quickly, and even when you think it has disappeared, the wind then changes and it’s back. As soon as you see it coming, you run.

This CS gas attack had taken place seconds before this photograph was taken, in a burnt-out sorting office in the Little Diamond area of Derry. We were jumping off the wall to get away from it. There had been a riot, and I remember we were trying to help some older people get away. I was 14.

I was aware of someone about 500 yards away, taking pictures. The photographer Don McCullin was dressed in a combat jacket with a big camera; he looked very different from the local press, who were always in suit jackets. McCullin was on assignment for The Sunday Times Magazine, and this image was first published in December 1971, as part of a story called War On The Home Front. It’s now part of the Tate and National Galleries of Scotland collections. I first saw it in McCullin’s book Sleeping With Ghosts, which was published in 1994.

I had moved to Derry a year earlier, from Portrush, a seaside town. It was a bit of a shock to be in a city, and the place was alive with politics: everyone was interested in it. I remember how dark it was, too – there were hardly any streetlights. There was barbed wire, helicopters hovering, soldiers on patrol and a lot of tension. I would go to listen to speakers such as the civil rights leader and politician Bernadette Devlin: as a boy, to hear her speaking was one of the most mind-opening things I had ever heard.

The following January, I was a steward at a protest march when British soldiers shot unarmed civilians: the Bloody Sunday massacre. The soldiers blocked the march, attacked and a riot started. I ran when the shooting began, but I witnessed what happened. That day traumatised most people in Derry, and it set the Troubles back 10 years. I was a witness at the Saville inquiry; I could provide a timeline of events, because I had been right there. I still have the civil rights armband I wore on Bloody Sunday, in a frame at home.

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Later, I was one of the original staff members at London Lighthouse, one of the first care centres for people with Aids. One of the men I worked with there was a former soldier who had been there the day of the massacre. He apologised. I’ve written a book based around that encounter, and hope to get it published one day. I’m now chief executive of a mental health charity in London.

Looking back at this photograph now reconnects me to those civil rights days, when we thought peace and non-violence would prevail. I went to the Photographers’ Gallery in London in the 1980s to see a show of McCullin’s work, and he was there, surrounded by people. To my regret, I didn’t go and talk to him. I would have liked to have told him how much his work had influenced me, how much I admired his views on war and his approach to humanity in taking photographs in conflict zones – and, of course, how our paths once briefly crossed.