"Let's have some fun," deadpanned Bloc Party singer Kele Okereke, halfway through last night's encore, before leaping into the crowd for She's Hearing Voices.

It was a moment that was as surprising as it was exhilarating, not least because Okereke had spent the previous hour hiding behind his guitar.

Not that he and the band should worry right now. For reasons not wholly clear, they seem to have conquered the United States with their blend of danceable, angular punk, which rarely troubles itself with a chorus.

And these prophets are honoured at home, too: they sold out Brixton Academy last night and they have repeated the trick this evening. So while they have their faults (Okereke's taciturnity; the absence of thrills or joy; their innate timidity), a band so obviously in their imperial phase also have much going for them and not just the fact that their current, second album, A Weekend In The City, is a great leap forward from their debut, Silent Alarm.

When the London quartet hit their stride on Waiting For The 7:18, The Prayer and Like Eating Glass (where Okereke again blossomed without that guitar), they slipped into a heroic groove.

Moreover, SRXT, the slow-burning suicide song that Okereke dedicated to his parents, was a welcome change of pace and Helicopter flew like the wind.

For all that, there was still something missing (bizarrely, it might even be confidence) and still little to explain why they have soared, but there were hints that they might just be worth persevering with.