Who's that singing? Matt Smith and Karen Gillan belt out a carol in sneak behind-the-scenes peek at Doctor Who Christmas special

By JODY THOMPSON A merry little Christmas: Katherine Jenkins, left, guest stars in the Doctor Who Christmas special alongside Michael Gambon, centre, and Matt Smith, rightIt's become as much a part of the celebrations as pudding, opening presents and the Queen's Speech - and now the cast of this year's Doctor Who Christmas special have revealed a sneak peak of just how festive it gets behind the