Ben Vautier's box has painted on it This box contains an idea so important that it could

Ben Vautier's box has painted on it "This box contains an idea so important that it could change art". We couldn't open the box even if we had the key because the box is now an exhibit in a glass case.Perhaps Lennon hit the imaginary nail on the head and Fluxus was always about banging imaginary nails into the coffin of the art establishment. There are, in the Royal Festival Hall show, some real nails with which the real British public have pinned to the wall Tube tickets, nappies and Hula Hoops packets. They have also written, amongst other things, "Yoko, you always were a bore and a Fraud", "What's with the arses?", "QPR - top London club", "The exhibition next door is better than this one", "Yoko Psycho" and "Adam, Fuck Me Now". It brought a smile to my face, so it didn't matter whether it was art or not, because here at last was something alive and funny and irreverent. Here was Fluxus.'Yoko Ono and the Fluxus Movement': 10am-10.30pm daily, Ballroom, Main Foyer, Royal Festival Hall, South Bank Centre, London SE1, to 23 Mar.

Those who know Radio 3 Controller Nicholas Kenyon may have noticed a glint in his eye in recent months. Is it glee, or terror? Probably both: after all, he has set himself, and the BBC, an extraordinary challenge for the next three years. Sounding the Century, a grand survey of music composed in the 20th Century, begins tomorrow night with a performance of that ultimate ground-breaker, Stravinsky's Rite of Spring conducted by Pierre Boulez, and lasts until the end of 1999 - plus a "morning after" celebration on 1 January 2000, with a mass premiere of new works by composers from 20 countries brought together under the aegis of the European Broadcasting Union As yet, not everything is in place. At this stage, Sounding the Century still looks like a steadily unrolling carpet, with certain elements in the pattern sketched out in advance, others still waiting to be woven in. As with the BBC's annual Proms season, overall responsibility for what goes into Sounding the Century has been handed over to one person - in this case, the composer George Benjamin. But, with just one person at the helm, can the series offer a truly balanced overview, or will the selection inevitably be partial? "It shouldn't be partial," says Benjamin - mindful, no doubt, of the flack Simon Rattle recently attracted when he left Elgar and Vaughan Williams out of his own personal survey of 20th-century music, Leaving Home, on Channel 4. "But, equally, I haven't been asked here just to make a dog's dinner of everything The project must have character, flavour to it.

Of course, all the major currents of the century will be represented, generously. But certain things will be covered which I think are important, which perhaps wouldn't have featured if someone else had been asked. Plenty of people are simply against modern music today, and if you'd asked X or Y to do it, they might have left out modernism altogether - especially post-war modernism. But the world would be so much poorer without some of that music."Yes, there does seem to be a growing number of people who want to pretend that the 20th century hasn't really happened - that it's possible to treat the "Death of God", Schoenbergian serialism, modern science and moral relativism as some kind of a bad dream from which we can now awake and go on as before."It's certainly the case in music," Benjamin agrees. "I heard a very famous conductor - a really big name - on the radio the other day saying that everything went wrong with Tristan There's a lot of narrow-mindedness and a lot of nostalgia.

I think one mustn't underestimate the effect of the end of the millennium on everyone's imagination. Think how most of us feel at the end of a year - the regrets as well as the attempts to look forward - and then translate that on to a 1,000-year scale! That must be one reason why people are more retrogressive than usual at the moment."Retrogressive thinking - or just "Back to Basics"? (Well, we all know what happened to that.) But Benjamin's language does seem to imply a moral position. Does he feel that in music there are good and bad, "healthy" and "unhealthy" trends? "That's not the kind of terminology I'd ever use when describing music. The story of 20th-century music is that there are diverse streams. Even if you take the 19th century, you find Mussorgsky, Verdi and Wagner working at the same time - all undeniably great opera composers and yet there's no neat way you can group them together. The diversity of the 20th century is one of its unique riches - the breakdown of common conventions, the growing liberty of the individual in society which is reflected in the arts - it's all to the good. It's partly for that reason that this is the century whose music I love the most, and my enthusiasm bubbles over at the thought of being involved in a project like this, and trying to represent the century fairly, rather than imposing an overall view that must be swallowed."One of the consequences of this century's increasing diversity is that it becomes harder to draw clear lines between High Art and Popular Art.

It could at least be argued that some of the classic jazz recordings of the 1950s and 1960s reveal a higher level of sophistication than much of the music being "composed" now. Does Benjamin think the old distinction is worth retaining?"Aaaagh! This is one of the anguished topics of the 20th century. Is serious music created in a purist's paradise of hermetic perfection, or do we prefer the postmodernist paradise of simply embracing everything? Both positions sound wonderful in theory, and both are - usually - extremely disappointing in practice. We'll be looking at the opening-up of the Western classical tradition to a whole load of influences that have shaken it up - Balinese gamelan music, Indian, Chinese, African jazz... You couldn't possibly ignore Stravinsky's jazz music - but that's still very much 'composed'. I do think there's a difference between art music and other kinds of music. That doesn't mean that one is greater than the other, but I do strongly feel that there is an evolving classical tradition, and I don't see why people need to put all the strands in one box."So was Sounding the Century born of a crusading spirit? As so often, there were practical influences too: 1997 sees the 50th anniversary of the Association of British Orchestras (ABO), an organisation that, of course, includes the BBC's own five orchestras, and it was in discussions among the ABO's recently formed Repertoire Group that the idea for this mammoth nationwide broadcast concert festival first began to take shape.