"This is the fifth date of the tour and we're still alive and healthy," grins Emily Staveley-Taylor, 29, the eldest of the Staves. "That's the kind of rock'n'roll band we are." The audience chuckle at the apparent irony. The sisters' two EPs (Mexico and the recent The Motherlode) suggest folk's answer to the Brontës, three demure, romantic women unlikely to pursue traditional rock antics. However, on stage they're three Watford sisters who bicker wonderfully, and talk mischievously about the venue's "fine whiskies".

Their easy-listening songs similarly have unexpected lurking depths. They're all beautiful and graceful, but at least one of them concerns "someone we really, really hate". Meanwhile, Pay Us No Mind is jolted from its serenity by a most incongruous "fuck".

But the ace is their voices, which mesh together stunningly, the product of singing since their teens. Perhaps importantly, they have one more set of vocal chords than not-disimilar sibling duo the Pierces.

Now under the wing of producers Glyn and Ethan Johns – who, between them, have worked with everyone from Bob Dylan to Laura Marling – the Staves' task is to rise above the pack. The Motherlode is perhaps too reminiscent of Marling's Rambling Man, but Icarus unexpectedly borrows a riff from Tyrannosaurus Rex's Debora. Arguably the best song of the night is In the Long Run, sung by young Camilla, who otherwise barely says a word. As the Staves demonstrate perfectly, sometimes it is the quiet ones you need to watch.