Where do you get your news from, and do you trust it to be true? For many of us, the answers to these questions are changing. Social media is an increasingly dominant source of information; long-established news sources, like the BBC, are in a fight for audiences and for trust too. Stephen Sackur speaks to David Dimbleby, who, in the course of a long broadcasting career, became the face and voice of the BBC on the biggest occasions, from elections to royal ceremonies. Can his journalistic values survive in a world where opinion so often trumps truth?