The High & Dry singer was a spokesman for climate change campaign The Big Ask in 2003 when he was invited to meet Blair at Downing Street as part of a Friends of the Earth get together, and the ex-Prime Minister's aides did not take kindly to the snub.
"It got into this big fight," he tells Telerama. "(They said), 'If you don't agree to meet the Prime Minister, Friends of the Earth will be denied all access to him'.
"Because of the Iraq war, I didn't want to do it. I felt it was morally unacceptable for me to be photographed with Blair."
But the singer insists he's still an advocate for environmental living - and he plans to continue leading by example, explaining the restrictions on him and his bandmates as they attempted to tour the world without leaving a carbon footprint kept him awake at night.
"If you have a Radiohead show where 20,000 people turn up, happy to see you play, and it's the only venue in the area and yet the promoter is saying, 'The only way to get there is to drive', you're faced with this decision and you're going, 'OK, do we blow out because there's no support or public transport and we deprive the fans of a concert in order to reduce our carbon footprint?'" he says. "Initially, it kept me awake at night, which sounds really stupid, especially when my second child arrived, in 2004. I got unhealthily obsessed with it.
"But when I started to get involved in doing something about it, that helped me a lot. But I always have the impression that I am not doing enough at all."