The highest-grossing US documentary of 2013 arrives on this side of the Atlantic with rave notices and an Academy Award nomination attached. For one night only, Morgan Neville's charming, feel-good picture shines the spotlight on the lesser-seen back-up vocalists the title describes. Some, such as Gloria Jones, are impossibly glamorous. Others, such as Merry Clayton, should have been contenders. Almost all, tellingly, are ministers' daughters who honed their dazzling ranges in gospel choirs. As Bruce Springsteen notes, it doesn't matter how talented you are, the 20ft between the lead vocalist and the supporting singer is a lot further than it sounds. Some of the director's subjects attempted solo careers; others have always been content with using their voice as a beautiful instrument in a grander ensemble. These gifted musicians don't always have it easy. Darlene Love, the sublime chanteuse who ensures, via Phil Spector's seasonal extravaganza, that all our Christmases are white, recalls hearing herself on the radio while working as a cleaning lady. Thankfully, this hugely enjoyable film puts Love and others up front and centre, where we feel they belong.