Alabama Shakes, Electric Brixton, review "Come on, Brittany!" is the cry that galvanises the room, coming from the stage not the audience. Brittany Howard's soulful holler to herself inspires everyone present to join in, exhorting 1,700 people to tell her to "ho-o-o-o-o-ld on!" On this evidence, the 23-year-old rip-roaring, foot-stomping, soul-baring talisman of the hottest band on the planet is holding on just fine. Alabama Shakes are experiencing one of those meteoric rises that takes the music business by surprise yet seems paradoxically inevitable, when everyone suddenly agrees that something is utterly fantastic, usually because it is. Last year, they were just a rumour on hipster blogs, slogging around the American circuit. This year, their debut album is top ten on both sides of the Atlantic, a support tour with British folk rock newcomers Dry The River has been upgraded to their own sold out headline jaunt, and the audience not only already know all the songs but are positively bathing the newcomers in worshipful adoration. What is most remarkable about the Shakes is that they are not doing anything new, or radical, or fashionable, or even obviously commercial. They play gritty, old-fashioned southern bar room rock'n" soul, the kind of mix of Stax and Sun first perfected by Creedence Clearwater Revival, only with less aggressive attack and an added flavour of Otis Redding courtesy of Howard's sweet, rasping voice. The tendency since the seventies has been to overload this kind of music with flashy lead solos, but Alabama Shakes lock into a groove and dig out the emotion. They do the small things well: splashes of Hammond and tinkles of piano (from session player Ben Tanner), fluid bass and solid drums pressing against the syncopated interplay of two guitars, lead man Heath Fogg's impeccable licks and flourishes weaving around Howard's agitated rhythms. They can work up a booty-shaking, garage-rocking stomp or take it down to a slinky, sensuous, heartcrushing whisper and it is all achieved with nuance and understatement. Their not-so-secret weapon is Howard herself, an unlikely frontwoman for this usually rather boysy genre. She attacks her guitar with bullying vigour and pulls gurning faces as she sings. Howard has the Adele factor that makes a mockery of music business marketing cliches, pure talent and charisma carrying her through against all prevailing trends. But the Shakes are not a vehicle for a diva to show off her melisima. They are almost the definition of a musical unit, locked in with Howard, rising and falling with every warble and fluctuation, surging when she lets rip and contracting to tender delicacy when she hits the sweet spot. Still only one album to their name, they don't quite have a repertoire equal to their talents. Amongst the showstoppers there are vaguely inconclusive fillers that make the right moves but don't linger in the memory. But give them time. Alabama Shakes are just getting started. When they really get going, we'll all have to hold on very tightly indeed.