We seem to have entered the twilight zone. Celestial harps and strange wooshes fill the air, and a disembodied voice croons: "What you see will defy expectation." In a sense, Jeff Tweedy's Wilco live up to this promise: in their first live show in London since 1999, they appear to be three entirely different bands.

For the encore, we have country Wilco, lolloping through Woody Guthrie's California Stars and a traditional folk song, and delighting fans of Tweedy's previous band, cult alt.country outfit Uncle Tupelo. For a third of the two-hour show, we see the MOR Wilco that Reprise, the band's label until last year, was hoping to beget when it asked them to make their songs more palatable for mainstream audiences. This Wilco revel in enormous riffs, fizzing drums and absurdly widdling solos; they radiate power-pop energy on Pot Kettle Black and turn I'm the Man Who Loves You into an outrageous rock monster.

And then there is the complicated, thrillingly experimental Wilco who caused so much consternation at Reprise. This band sound as if they are playing at the end of the world. The brooding Radio Cure is full of atmospheric disturbance, the weird whirrs of alien forces hovering among the stars. Ashes of American Flags opens with keyboardist Leroy Bach conjuring up a heat-haze gashed with vapour trails; when Tweedy starts thrashing savagely at his guitar, it feels as though the sky is going to crash through the venue's roof. When they play Misunderstood, from the 1996 album Being There, Tweedy's agonised, spitting vocal and Glenn Kotche's hammering drums could cleave the ground apart.

Tweedy's demeanour shifts with every musical twist: he looks oddly demure for the country songs, grins at bassist John Stirratt when things take a summery turn, glowers when the sound fractures and storms. But he is consistently enigmatic, coolly distanced from the audience, punctuating his bleakest lyrics with disconcertingly nonchalant gum-chewing. It isn't until the encore that he starts loosening up, admitting: "I'm afraid to say anything in London, I've said a lot of stupid stuff." His reserve makes the tricksier songs icy and makes it surprisingly difficult to connect with the band. Experimental Wilco are an excoriating experience; they need a little of country/MOR Wilco's simple joyfulness to strike the heart as much as the head.