THERE WILL be two enormous religious gatherings in London tonight. At Earls Court, an American evangelist who claims to have healing powers will attempt to cure the sick using prayer, while in Wembley Stadium, four Irish Catholics who claim to be reborn in the flames of irony, will minister to 60,000 believers via a rock show. Both will vividly illustrate the human need for acts of faith, but only one of the shows has a hospitality tent. That's the one I saw last week.

The U2 'Zooropa TV' show at Wembley invokes the Church of Rome from start to finish. Every stage of its superb production reverberates with majesty, guilt, suffering and solitude, with idealised love and desire. U2 have always traded on a certain Celtic mysticism, and despite going all hi-tech and clever, their sacerdotal roots are never carefully concealed. Halfway through, you can practically smell incense.

With most religions, sin precedes remorse. The enduring mystery of Catholicism is that you can skip all the sinning and cut straight to guilt. So we start by confessing, as all good Catholics do. On stage, huge video screens flicker with looped footage from Leni Riefenstahl's Triumph of The Will, a sardonic nod to the parallels between stadium rock and the Nuremberg rallies.

The service begins, U2 perform their hymnal rock. There is an explosive interaction between performance, screens and lights. Bono's 60ft televised image follows every move, extolling simulated pleasures that are 'even better than the real thing'. Irony? I thought one eyebrow would never come down.

His back to the audience, Bono tunes the giant screens to satellite TV channels. Picture this: 50,000 people staring past the man on stage with his back to them, at the screens towering above him. Christ] He even holds the remote control with two hands, as if he were consecrating a chalice. Perhaps when so many people stare at a vertical surface, it simply becomes an altar. And if television is the new religion, why watch at home when you can share it al fresco with 50,000 others? The crowd roars its approval.

Next, an error that almost cost U2 the crowd's goodwill: a live satellite link to Sarajevo. On screen, three Bosnian women - Muslim, Serb and Croat - testify to their enduring friendship. Unexpectedly, one of them addresses the audience: 'I want to ask you people, what you do for us? Nothing.'

A cloud of shame hovers as Bono turns back to us, and the band plays its slickest riff so far. Will our guilt be absolved by this bell-like guitar, these incantations, this vast, droning sound? I think not. If Bono wants to be the Bob Geldof of Bosnia, I'm right behind him. But if he's not ready to go all the way, to provide a focus for the anger that ordinary people feel - if he's not prepared to go out there and stop the war - then he should paddle back down to the shallow end.

Of course, the crowd forgives him, and suddenly it's clapping practice for everybody, as the U2 sound straddles the divide between rock and techno: stadium-sized dynamics and a hypnotic pulse. It is no coincidence that U2's best work bears the stamp of Brian Eno, pioneer of ambient music, and techno savant. 'Where The Streets Have No Name' induces instant euphoria, as U2 do what they're best at, slipping into epic rock mode, playing music made for the arena.

Fifty thousand people jump and clap and sing in frenzied unison, proving that religion isn't dead, it just smells funny. For U2 undoubtedly fulfil a spiritual yearning in this crowd. The same need attracts kids to large outdoor raves and football fans to outsize stadiums: a ritual celebration in which the self is submerged, a surrender to collective ecstasy. Here is the closest thing to orgiastic, religious hysteria that our society will sanction. And it is to U2's credit that they acknowledge this. It also explains why they sell so many records.

They follow with 'In the Name of Love', still their best number, the song that made them. The power surges now, you can feel it through the blue plastic seats. Bono leaves the chorus to the crowd, and Martin Luther King appears on screen, delivering the final lines of his 'Promised Land' speech. And then they're gone.

The matter of transubstantiation remains. So we watch a series of videotaped 'confessions' (geddit?) made earlier by members of the audience, now televised. A cheery fellow reflects on his girlfriend's surprise when she finds out what he has been up to with her husband. The band, which has crept back on stage, slams into 'Desire'.

I came as a sceptic, and left believing I had witnessed the most sophisticated meeting of technical wizardry and mojo priestcraft ever mounted. I'm not embarrassed to say I enjoyed U2's skilful manipulations. But speaking as a devoutly lapsed Catholic, I do feel kind of guilty.