Paul Gravett distributes leaflets in McDonald’s with undercover police officer, Bob Lambert, 1986

I apologised under duress. Needless to say there is absolutely no way I would have said sorry had I known Lambert was a spy

I met Bob Lambert at my first London Greenpeace meeting in 1985, when I was in my early 20s. We got chatting about animal rights and quickly became friends; he was charismatic and like the older brother I never had. He was someone I could identify with; he was amiable, vegan and believed strongly in animal rights. He'd drop little compliments. One that stands out was at a benefit gig for the Animal Liberation Front in September 1986, at a squat in Islington. I designed the poster and he said, "That looks great. You're an artist!" I was flattered, and it stuck with me. I now know that spies are trained to tell you things you want to hear.

This photograph was taken on World Anti McDonald's Day. We'd just published a new leaflet entitled What's Wrong With McDonald's: Everything They Don't Want You To Know. I think I contributed one sentence: "Revolution begins in your stomach." It was the leaflet that led to the McLibel trial - I was one of those sued by McDonald's in 1990.