To be honest, that perpetual question, "Can Music Make a Difference?", is one that I don't consider much. Even if music can't, that shouldn't stop us from trying. Also, when you've written a political song, how can you ever gauge if it has made a difference? It seems to me that the relationship between music and change is more complex than simply the singing of songs.

For instance, at a concert in New York a year or two ago, a guy came up and gave me his card. He was a labour lawyer and he told me that this career choice was a direct result of my music. Now, that made me feel pretty proud. But upon reflection, I felt that such a phenomenon could be looked at in a number of different ways. For instance, has my skill as a songwriter ensured that there are better labour relations in the New York area, or did I just provide the soundtrack to this guy's vocation? After all, it's not me out there defending people in the workplace, is it?

Was that attorney an activist drawn to Billy Bragg or did Billy Bragg make him an activist? Ask yourself the same question: I bet your answer is similar to mine. I was drawn to The Clash because I had a certain worldview and wanted that to be reflected in the music that I listened to. I read their interviews and checked their lyrics, but I suspect that Margaret Thatcher was a bigger influence on my political development than The Clash.

Which is not to dismiss the politicising effect of punk. The Clash opened my mind to the dynamic possibilities of political popular culture and, in doing so, they undoubtedly changed things for me. They didn't change the world but they did change my perception of the world. And it was because of my disappointment in the failure of bands like The Clash to change the world that I became the kind of performer prepared to take a stance against Thatcherism.

This suggests that music does not have the impact of an event, which changes the world instantly and tangibly, but is more akin to an idea, which works in a gradual way - making small subtle changes that build up over time. In that sense, music can be a catalyst for change, particularly social change. Think of Elvis mixing black and white culture in Memphis in 1954, or the Two-Tone ska movement that emerged as a direct response to the rise of the neo-Nazi National Front in England in 1979. However, music can only perform this role in conjunction with genuine forces of change within society.

Maybe a song of mine changed the perception of our New York labour lawyer friend. Maybe he just enjoyed jumping around in his bedroom to "Help Save The Youth Of America. Whichever way you look at it, one simple fact remains: it is up to the audience to change the world, not the performer.