"Last time I played here, it was dirty," says Pete Townshend, of his glossily refurbished surroundings. "Now it's clean - and I'm dirty." An ambiguous remark, given that he recently walked out of a Howard Stern radio interview when Stern mentioned the internet-porn furore of several years ago, but the Roundhouse crowd greets it with the reverent approval that follows all his pronouncements.
Tonight's show, the closing-night jewel in the crown of the BBC Electric Proms, sold out in 35 minutes. Though they are literally half the band they once were, Townshend and Roger Daltrey are a rock-solid team, so attuned to each other's presence on opposite sides of the stage that they barely exchange a glance. Their spirits are youthfully peppery, and Daltrey is a microphone-twirling, air-punching marvel.
They are touring to promote their first new album in 24 years, Endless Wire, a 21-track affair containing Townshend's new "mini-opera". Rumours that they intended to perform it all in one solid lump prove mercifully unfounded. Eleven new tracks are sprinkled among classic hits, and Daltrey dispatches them all with the same dollop of raspy love.
Of course, it is the hits that show why the Who deserve their place on rock's super A-list. My Generation and I Can't Explain, sung against footage of swinging London and poignant close-ups of Keith Moon and John Entwistle, are 41 years old; Pinball Wizard is 37 and Baba O'Riley 35. All still sound fresh today; Townshend, arms windmilling, and the stomping Daltrey are 60-year-old adolescents, still in thrall to rock'n'roll.
The decision to close the show with the new album's watery Tea & Theatre is inexplicable, especially coming right after a brilliantly monumental See Me, Feel Me. However, it serves to underline the glory of their back catalogue.