British Sea Power, Embassy of the Czech Republic, London

"Welcome to the Czech Republic," says the singer, Yan (aka Scott Wilkinson). A band called British Sea Power taking over the Czech embassy fortunately only sounds like a Victorian imperial adventure. This wonderful Brighton-based band's interest in other places and times is far more open-minded and benign. Their third album, Do You Like Rock Music?, being launched tonight, is as comfortable describing half-century-old Essex disasters as it is welcoming drunk Polish immigrants. Recalling rock'n'roll's founding tradition, it draws on unthreatened British roots that are only enriched by each further culture they touch.

We are in a Seventies conference room, not a grand ambassador's residence, with embassy staff dancing in the crowd as red buses pass by the window. The band play in a state of disciplined ecstasy, heavy on whoops, chants and clatter. They pervert sonic blueprints laid down by post-punk bands such as Echo & the Bunnymen or U2, while drawing on their own humbly mythic British vision. "Lights Out for Darker Skies" is its most poetic expression, imagining stars reappearing over a neonless Britain, as Yan declares: "The future's twisted, righteousness is coming back around." "Lucifer No" says this still more simply, rejecting evil with Big Daddy's old wrestling chant, "Easy, easy," already adopted by the crowd.

But "Waving Flags" is the night's defining moment. "You are astronomical fans of alcohol... so welcome," Yan sings to the East European immigrants currently entering Britain under a xenophobic cloud. In this embassy, of course, the situation is reversed. Union flags have rarely looked so inviting or untainted by nationalism, as Czech signs are waved among them.

The band begin a post-punk rave-up, and guitarist Noble steps trustingly on to his fans' hands. He bends, mid-air, into the music, then takes London's diplomatic quarter off the gig circuit for another decade by hauling down a light. Unlike Keith Moon, he tries to put it back. As a snapshot of BSP's rock idealism, it isn't bad.