Pop / FLEADH Finsbury Park, London

The post of Lunatic Genius brings with it many duties - snubbing national anthems, desecrating pictures of religious leaders. So no wonder Sinead O'Connor's appearance at the Fleadh on Saturday evening was so rare; she must have her Filofax packed with stunts to make Salman Rushdie look like Nanette Newman.

The Pope was safe from her wrath tonight, though. For a whole hour, we were reminded of the Sinead O'Connor who first put the fear of God into us eight years ago. She has grown her hair out now, so she's more tomboy than Isle of Dogs skinhead, and her blouse burned white-hot in the dusk, singeing the eyes. The voice, meanwhile, set to work on your ears.

On "The Emperor's New Clothes" she lowered it to a murmur before howling the line "I will sleep with a clear conscience", with a cheeky smirk and no little irony. "Red Football" was unleashed with stinging vitriol, the stage ablaze with light, her face gnarled with rage, while her delicate delivery of the honey-flavoured "John, I Love You" was profoundly moving, its chiming refrain - "There's life beyond your wildest dreams" - hanging like incense in the chilled night.

It's comforting that, after all the suggestions that she had lost her marbles, O'Connor has clung onto a voice that not only wakes the dead, but brings tears to their parched ducts. You had better get acquainted with her music - one day your grandchildren will be asking you about her.

Your own grandparents may be the people to quiz on Van Morrison, the gruff Fleadh stalwart who made the afternoon feel so warm. His was an effortless seduction, coming after the wretched Saw Doctors, who peddle music to slap your thigh and spill your pint to (you'd describe them as "salt of the earth" and not mean it as a compliment).

Morrison, playing a rheumy saxophone and wailing with unkempt passion, was joined by Brian Kennedy, a mane-haired singer with a lush velvet voice and a suit to match. When Morrison announced "here's one from the new album", most people seemed to think he'd said "make a stampede for the bar", but that was inevitable. It was a fool, though, who was getting the Guinesses in during the magnificent 10-minute-plus arrangement of "It's a Man's Man's Man's World" or the gentle patter of "Whenever God Shines His Light", a title which begs the rejoinder "He has to ask Van if it's OK with him".

The Beautiful South, who topped the bill, practice the sort of joke you expect Jeremy Beadle to have masterminded. The gag is this: their lyrics are spitefully accurate indictments of blind love, camouflaged by jolly horn sections and tinkling pianos. Musical Mickey Finns; drugged meat. It's a good joke. But it's their only one (if you don't count singer Paul Heaton's dreadful onstage gag about his stripy trousers, and I wouldn't).

The set's sharp edges proved that few other bands can match them for cruelty: "We Are Eachother" probes an obsessive romance whose participants are indefinable from one another; "Tonight I Fancy Myself" chooses masturbation over just such a relationship. But on a day that was buoyant with celebration, it felt cheap and grubby to be giggling at people just because they send joint Christmas cards and call eachother "baby", no matter how jolly the horn section made it all sound.