Daniel Johnson: Ian, is it possible to combine celebrity with musical integrity? Your face is visible on the London Underground and everywhere we look. Is it possible for a musician nowadays to become a household name and yet still be serious about his work?

Ian Bostridge: Well, in classical music it's a very minor form of celebrity, so it's not particularly undermining in a way that I think it can be when you're doing something and you're very famous. I think being commented on has an effect - and it's true for writers as much probably as for performers, except that performers, if they read their reviews, have to put up with it all the time. It's this endless commentary, and it makes you aware of what you're doing. You talked about integrity, and I suppose it's about trying to stay true to what you think you should do, for yourself, while at the same time absorbing outside influences. Being open to criticism, but at the same time sticking to your guns if people hate what you do.

DJ: Tim, your new book is about the triumph of music. How far do you think that triumph has turned into triumphalism, that in a sense music has changed as a result of becoming such an enormously important force in the world?

Tim Blanning: Well, that's a very good question. I suppose that the fact that I've written a book called The Triumph of Music is a triumphalist statement in its own right. But looking at the practitioners of music, I think that there certainly is a triumphalist air about, in that musicians now do take themselves really very seriously indeed - especially at the popular end of the spectrum.

Classic cases would be Bono and Bob Geldof - both of them Knights of the British Empire incidentally - who, when they speak to the President of the United States or the President of the World Bank or the Prime Minister of the United Kingdom, expect to be listened to. A great example is the G8 concerts that they organised in 2006. These were accompanied by marches and demonstrations, and the concerts were there to put pressure on governments to make a pledge to do something about Third World debt. And it had an effect.

So they do take themselves very seriously and they expect to be listened to, and they are listened to.