Consummately sweaty and rocking, these Californians have come from nowhere to roost at No 5 with their impossibly catchy new single, In This City. Unknown in America, they've relocated to London, where they have already been evicted from a flat because of noisy partying. After seeing their first headlining show in the capital, you have an inkling of what the neighbours must have gone through.

The five members - there is no Iglu nor Hartly - are dedicated to raising the roof, whether via their bass-heavy pop-rap attack or by inviting "all the hot chicks" on stage. Frontmen Jarvis Anderson and Sam Martin - quintessential LA dudes in surfer vests and long, straggly hair - are tireless stirrer-uppers. Pounding rickety keyboards and rapping as only nasal white men can, they get the party started, then refuse to let it stop. Guitar and that gut-crunching bass create an irresistibly melodic foundation, and the whole good-natured but socially conscious (the opener is the relatively politicised Violent and Young) mess is the closest thing 2008 offers in the way of a 1980s Beastie Boys experience.

There are only nine songs in the set, of which one is a "brand new fuckin' song" that imposes a swooshing, space-rock respite from the chaos. Moved by prog-style flakiness, Anderson directs: "Every-body close your eyes and meditate." Suitably recharged, he is soon pointing and jabbing through In This City's tinny chorus. A beaming boy climbs on stage to join him and is promptly pushed back into the crowd by Anderson, but when the kid reappears during the Eminem-meets-McFly mash-up Day Glo, he's allowed to stay. Well, it would be rude not to admit fans to the party.