Tortoise/ Coldcut vs Lee 'Scratch' Perry/ The Bees, Royal Festival Hall, London

Shimmeringly beautiful, transcendentally dull - the magic of a Meltdown moment

According to my dictionary, a meltdown is an "unforeseen and disastrous failure, with possible wide-reaching effects". Hmm. Wonder if the people at the Royal Festival Hall were aware of that when they asked reggae legend Lee "Scratch" Perry to curate this year's Meltdown festival? A small "m" certainly looked on the cards when the posters for tonight's shenanigans went up just in time for the Beta Band to realise they were supposed to be somewhere else. Still, no problem, no problem, The Bees swarmed by just in time for what, on paper, looks like the most intriguingly diverse of this year's line-ups.

And what a lively way to open the evening this group from the Isle of Wight prove to be. Centred on two friends - Paul Butler and Aaron Fletcher, who grew up in an isolated community and write songs in their garden shed - The Bees sound is a glorious mélange of styles best described as sunshiny, trippy, dubby pop. The seven musicians swap instruments with alarming dexterity till the horn player's the drummer, the drummer's on bass, the singer's running about like a kid in Willy Wonka's factory and the sound never collapses under the weight of The Bees' musical ambitions. They are truly a meltdown unto themselves.

Then, faster than the bar staff can pour a pint of Guinness, the stage is cleared to reveal a bank of technical equipment that would put PC World to shame. The five giant screens behind light up with an image of Andy Warhol holding a television screen displaying the Coldcut logo, and we settle down for an "audiovisual zentertainment" entitled Sex, Dub and Rock.

Coldcut - essentially a former art teacher named Jonathan More and his computer programmer sidekick, Matt Black - first sprang to prominence way back in 1987 with a devastating and groundbreaking remix of Eric B & Rakim's "Paid in Full" that married Ofra Haza's Yemenite chanting with an already classic hip-hop moment. It's astonishing to think that even now, over 15 years on, that record is still a DJ record-bag mainstay, guaranteed to make people jump out of their seats.

Founders of the Ninja Tune record label, Coldcut are still cutting and pasting and mixing, matching and mashing-up the wildest elements into an entertainment that is equal parts rock-the-house and give-these-boys-the-Turner-Prize now. Tonight's "show" splices Clinton speeches to "Magic Moments", to The Jungle Book, to the theme tune to The Good, the Bad and the Ugly, to multi-coloured psychedelic footage of tonight's curator. It's both so retro and so far ahead of its time that who cares if the six people shuffling from computer screen to computer screen on stage look like a Swedish design company excited by a new account?

The biggest cheer of the evening greets the footage of Prince Charles learning to "breakdance" in Brixton. The biggest cheer, that is, until "Scratch" himself ambles on, incense burning, dragging a red suitcase on wheels with a Fisher-Price toy in his other hand. "Welcome to my techno, hepno, erectno party," says the man behind Meltdown, summing up events as only he can. A couple of "numbers" - bubbly dubby streams of consciousness, actually - later and Perry is off, promising us that, "This old man refuse to get old, refuse to sell his soul, refuse to be weak, refuse to be a freak." Unique.

So then we get Tortoise. Can the "post-rockers" from Chicago possibly follow all that has gone before them? And how best to describe the sound they make? Well, not with words such as chorus, verse, harmony and melody, that's for sure. This musical impressionism, this jazz-leaning free-flow that is actually unbelievably structured and mathematical, is sometimes shimmeringly beautiful and other times transcendentally dull. A brief glance around the auditorium reveals more index finger to temple action than your average university lecture room. Luckily, by the time you notice that your chin is sore, it is over, slightly anti-climactically.

Perhaps this is exactly how Meltdown should be - pushing envelopes, toying with received wisdoms and generally making a fool of formulas. Maybe, this is precisely what entertainment should be in the 21st century. Clearly, this is the Meltdown that the dictionary hasn't cottoned on to yet.

Meltdown continues on the South Bank to 30 June. Box office: 020 7960 4242