Their 2009 Mercury prize nomination briefly trained a spotlight on Sweet Billy Pilgrim's electrofolk, but it swiftly moved on when the Buckinghamshire trio failed to win. Left to their own devices, they have added a new dimension by taking on singer and guitarist Jana Carpenter, whose vocal harmonies turn their rather cerebral brew into something vibrant with longing and regret.

But as they face a few hundred punters in the back room of a bar-restaurant in east London, they are keenly aware it will take more than a rejigging of their sound to boost the bums-on-seats count. "Thank you, Castle Donington," said leader Tim Elsenburg – sardonically, presumably – to the fans, after they had ecstatically greeted a string of tracks from the forthcoming album, Crown and Treaty. "You're the early adopters. Bless you all for coming."

Yet there was so much going on in each song – so many genre-bending jerks and twists – that it was hard to see how the band will achieve their longed-for breakthrough. Beautiful as it is, the new song Blood Is Big Expense, with its melding of soft-rock guitar licks and rugged folk harmonies, is the definition of "niche". Likewise Future Perfect Tense, the only song played from Mercury nominee Twice Born Men: it hopped from Latinate swing to crazed thrash-out, finally petering out into a three-guitar jazz noodle.

In the midst of all this baking and blending was the core ingredient: Elsenburg's lost-soul keen and Carpenter's oak-smoked alto. Combined, they were the heartbeat of the night – a surprise a cappella cover of Whitney Houston's I Wanna Dance with Somebody was a-quiver with yearning.

Nevertheless, Radiohead and Elbow started out with similarly square-peg music, so who's to say that sweet, bespectacled Elsenburg and his band won't strike a chord among a wider audience of thirtysomethings who appreciate a group with smarts?