At the BFI Imax, in the context of a TV festival leading up to the centennial of the BBC and before a sell-out audience, Alan Yentob engages Stephen Fry - writer, presenter, comedian, actor - in a wide-ranging discussion of the deeply personal challenges he has faced, and the professional achievements he has enjoyed, in his extraordinary life so far, from his jail time as a teenager convicted of credit card theft to his four-decade relationship with the BBC.