"Welcome to the Czech Republic," says the singer Yan considerately.
A band called British Sea Power (BSP) 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. On their first album, their Sussex location encouraged a collaboration, with not Fatboy Slim, but the county's ancient folk guardians, the Copper Family. Their third, Do you Like Rock Music?, being launched last night, was recorded in a Cornish fort during army manoeuvres in rural Suffolk, Canada and the Czech Republic. It is as comfortable describing half-century old Essex disasters and welcoming drunk Polish immigrants.
In Rock '*' Roll's founding tradition, it draws on unthreatened British roots, that are only enriched by each further culture they touch.
So standing on Czech soil, in an enclave of East European embassies in west London, is as perfect a place to find British Sea Power as any of the caves and woods they've played in the past.
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. It seems surreal enough, as Yan sings of "a bright and haunted age" on "Atom" and a violinist and sampled air raid sirens combine in sawing cacophony.
British Sea Power play in a state of disciplined ecstasy. Heavy on whoops, chants and clatter. They pervert sonic blueprints laid down by post-punk bands from Echo & the Bunnymen to U2, while drawing on their own humbly mythic English landscape.
And the result, on Do You Like Rock Music? is a hopeful, eccentric vision unique in pop.
"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".
He says this still more simply, rejecting evil with Big Daddy's old wrestling chant, "Easy, easy!", already adopted by the crowd. When the past is invoked, in the unspecified 1953 catastrophe of "Canvey Island" there is a feeling of pleasant, overwhelming oblivion.
But new single "Waving Flags", addressing the present head-on, is the night's proudly defining moment. "You are astronomical fans of alcohol... so welcome," Yan sings of the East European immigrants currently entering Britain under such a xenophobic cloud.
In this Embassy, of course, the situation is reversed. And the Union flags draped on BSP fans have rarely looked so inviting or untainted by nationalism, as Czech signs are mixed among them. The sampled sound of a plane landing sounds dangerously close in this small room.
Then the band begin a post-punk rave-up, riffing around garage classic "Louie, Louie", as guitarist Noble steps trustingly onto his fans hands. Soon, he is bending, mid-air, into the music, until he takes London's diplomatic quarter off the gig circuit for another decade by hauling down a light. Unlike Keith Moon, he tries to fix it.
As a snapshot of this band's 21st century rock idealism, it isn't bad.