Mumford & Sons: O2 Arena, London, review As the lights go down in the O2 Arena and four silhouettes appear behind a red curtain, there is a surge of anticipation rising to a proper, old-fashioned, ear-shattering roar of excitement. Then the curtain falls and there they are, the least likely stars of the 21st century: four beardy, scruffy young English folkies, one of whom is thrashing a banjo, another whacking an acoustic guitar whilst banging out time on a bass drum, all pulling gurning faces as they charge into their opening song with the gusto of gang of rabble rousers at a drunken hootenanny. Mumford & Sons are a bit of a mystery. In an age of digital urban electro dance pop, all techno bleeps, plastic beats and sexy viral videos, how did a group of avowedly old-fashioned acoustic roots musicians come to be the biggest new band in the world? Their second album, Babel, went straight to number one on both sides of the Atlantic, the fastest selling album of 2012, and the posh British boys ended the year with six Grammy nominations, including Best Americana Album. It's as if Newcastle suddenly discovered an appetite for imported coal. "It's been a weird year for us," acknowledged frontman Marcus Mumford, welcoming 20,000 fans to their "end of year party." He looked tired and drawn from the outset, perhaps a consequence of the endless touring that has accompanied their meteoric rise. Mumford and his band mates are almost always at full pitch, the kind of musicians who play like every note causes them physical pain. There is not a lot of subtlety to the Mumford oeuvre. In their own way, they are as formulaic as Oasis or Status Quo, albeit with a slightly broader musical palette. Although they swap instruments, picking up accordions and plugging in electric guitars while string and horn players come and go, they really only have two speeds: slow and stripped back and fast and thrashy. The best of their material switches between these two modes in a way that seems to marry the sacred (the almost holy ambience of their tremulous four part harmonies) and profane (the sheer rambunctious release of their Celtic foot stomping hoedowns). Like U2 and Coldplay, bands who thrive in these big spaces despite the derision of critics, Mumford & Sons have the power of sincerity, making every possible effort to forge the most positive and uplifting connection with their audience. Their songs address existential and emotional dilemmas in broad poetic language and Marcus Mumford never forgets to include a singalong chorus. It is as accessible as the cheesiest pop but delivered with a raw, organic sound that has struck a chord with listeners apparently alienated by the synthetic values of most modern pop. No one picks up a banjo dreaming of superstardom but Mumford & Sons have stumbled onto a new genre and found it was just what the world was waiting for: stadium folk.