Roger Waters, the composer and multi-instrumentalist, is speaking in a London club about recurring themes in his work, from Pink Floyd's album masterpiece Dark Side of the Moon to Ça Ira, the opera about the French revolution he has just finished, via The Wall, the concept album to end all concept albums.
But he might as well be talking about himself. Waters is often cast as the musician who started the longest feud in rock when he unilaterally declared Pink Floyd finished in 1983. Four years later, Waters sued guitarist David Gilmour, drummer Nick Mason and returning keyboard-player Rick Wright when they decided to carry on as Pink Floyd. He lost the case, despite having contributed the most creatively after the departure of Syd Barrett, the original front-man, in 1968.
Waters, the bassist, went off in a huff, punctuated by the odd solo tour and album and a spectacular production of The Wall in 1990 after the fall of the Berlin Wall.
When fans heard that the classic Floyd line-up would reunite for Live8, many didn't believe it would happen. Waters, who recorded a song called "The Tide Is Turning (After Live Aid)" on his 1987 album Radio K.A.O.S., was keen on the idea. In 2002, Mason had twice joined him on stage to play the epic "Set the Controls for the Heart of the Sun" at Wembley Arena, London.
"Those were good nights," Waters says. "It was sort of a precursor to the rapprochement. Nick and I were always friends when we were in the band. After we sort of broke up I said a few harsh words, but we became friends again a few years ago.
"But Nick didn't have the power to mediate," Waters says about Live8. "Bob Geldof asked Dave, who said no. Then Bob saw Nick at a party, he sent me an e-mail, and I called Bob. A couple of weeks later, Geldof got me Dave's number and I called him. He was very surprised when he answered, but we had a good conversation, and 24 hours later he called back and said, 'Let's do it.'"
Waters approached rehearsals in a positive frame of mind. "There was a certain edge at the beginning, but I decided I wasn't going to have a confrontation. If there was any problem, I would just roll over. It worked very well.
"I was quite open about wanting to do 'In the Flesh' from The Wall because I sing it, but Dave wanted to open with 'Breathe' from Dark Side of the Moon. I went, 'OK, I don't care that much.' Anyway, I sang a bit of 'Wish You Were Here' and I sing on 'Comfortably Numb', and we did 'Money', which seemed appropriate for the occasion. I mean, I wrote the songs, these are my words and a lot of my music. We all made different contributions to something we did together all those years ago, and it was really good, so why not celebrate it?"
Three months on, Waters can't help enthusing about the Floyd reunion, soon to be available on the Live8 DVD. "It was terrific. It was really good fun and the music sounded great. Dave sang and played beautifully, I managed to croak out my bits all right, we all played in tune, so it was good. I've seen a rough cut of the performance and I'm really happy because the DVD is going to raise tons of money.
"It was a great weight off my back to have a rapprochement with the three guys after all the enmity. Constantly, in my work, I am exhorting people to let go of entrenched positions, and that could be seen as hypocritical in view of the fact that, for all those years, I held an entrenched position in terms of the history and the internal politics of Pink Floyd.
"So to be able to relinquish that enmity was very important to me. If that's the only time we play together for the rest of our lives, I will reap the benefits of those few days for the rest of my life."
For now, Waters's attention is focused on Ça Ira, an operatic history of the French Revolution in three acts. The bass-baritone Bryn Terfel takes on three roles, including Louis Capet, the King of France; the soprano Ying Huang sings the iconic Marianne role and Marie Antoinette.
The grand projet began in 1988 when France's leading lyricist Etienne Roda-Gil and his wife Nadine showed Waters a libretto and some striking illustrations. "They had the whole thing in a box, about 50 pages. Every page had a painting by Nadine. They pitched me and I was hooked.
"The original idea was for Ça Ira to be part of the bicentennial celebration of the French Revolution in 1989. I set the libretto to music. In six weeks I had a demo of the whole thing mapped out on a cassette, a mix of what I'd recorded with me singing all the parts and playing all the instruments. François Mitterrand was keen and suggested the new Opéra de la Bastille should put it on, but Daniel Barenboim was fired and this thing written by an English bass-player foundered on French chauvinism.
"I resisted pressure to write an English version, but I kept going back to it and eventually I relented," Waters says. "I did a concert for the Countryside Alliance in 2002, and the Royal Philharmonic Orchestra performed the overture from Ça Ira. Etienne came over and it was very moving. He said to me, 'It's much better in English.'"
Waters admits that "some Floyd fans will get it and some will be disappointed," but stresses the relevance of Ça Ira. " France in the 1780s is a microcosm of what's going on in the world. At the top, there is a monarch, or somebody very powerful like George Bush or Tony Blair, and a small political hierarchy, and then the rest basically have fuck all, live on a dollar a day. The conditions are ripe for a bloodbath.
"The only realistic option is to divide the cake differently. After Live8 and the G8 summit, at least people are beginning to make noises about changing the deep imbalance in the world," says Waters, who lives in Manhattan. "I come back to the UK quite often. I didn't leave as a protest against the hunting ban; I was following a child in the wake of a divorce."
Waters remains passionately anti-war. The death of his father at Anzio during the Second World War has been a theme in his work, especially on The Wall and The Final Cut. Waters released two new tracks, " To Kill the Child" and "Leaving Beirut", on the internet as a protest against the war in Iraq last year.
Waters winces when I mention the offers - $150m! - the reunited Pink Floyd have been made to play US dates. "Whether we'll play together again, I have no idea," he says diplomatically.
'Ça Ira' is out on Sony BMG Masterworks/Columbia. The Live8 DVD is out on Warner Vision on 7 November