Lucy Rose, Hoxton Bar & Kitchen, London

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Judging by the queue outside and the 100 fans packed within, the unsigned Lucy Rose is proof that internet phenomena are still occurring.

Early Myspace demos have attracted serious global attention, including from indie star of the moment Jack Steadman from Bombay Bicycle Club, who has already remixed one of Rose's songs and is in the audience tonight.

The elfin 20-year-old Rose has swum around the dive-bar circuit as a solo singer-songwriter for a year, but now she's taking to the stage as part of a five- piece band complete with a dreadlocked rhythm section (the Bhebhe brothers, Simba and Beanie) and moustachioed dudes Henry Broadbent on keyboards and Adam Coney on electric guitar. Visually, they're a misfit urban youth gang fronted by Joan of Arc gone indie ingenue. Musically, the armour of current pop contrivance is noticeably missing.

Rose has a beautiful, subtly textured voice, as distinctive in its way as Florence Welch's but without grandstanding tendencies, and her songs have a hooks-and-heartstrings classicism that makes her hard to label. The sweetly circling opener, "All I've Got", surprised with it's vaulting indie chorus. "About You" veers towards 70s West-Coast rock, and "Be Alright" backs together chords that Lennon and McCartney would've been proud of. With the power of the band behind it, "Be Alright" transcended its East End surroundings – you could imagine it on a festival stage somewhere, delighting thousands.

But the centrepiece is Rose's voice, a beam of husky starlight which could work as well with an orchestra as with a banjo. Opting to downplay her chatty side, she was content to make the odd quip about her band's moustaches, have a swig of her Guinness and just play the songs. "Amsterdam" is effortlessly cool and manages to rescue pop reggae from it's disreputable corner and the epic finale – the guitar-walled tsunami of compassion "Don't You Worry" – is simply astonishing and sung directly from the heart.

Not many 20-year-olds can pull off a night of cross-genre, contrivance-free, elemental musicality, but tonight, with a hint of Marianne Faithfull here, a flavour of Beth Orton there, and nonchalant confidence everywhere, Lucy Rose did just that. If the Lady Ga Gas of the moment don't do it for you, then fear not: Lady La La has arrived.