Guardian editor Alan Rusbridger talks to BBC arts editor Will Gompertz at a preview screening of The Fifth Estate on Monday 7 October about the implications of publishing the National Security Agency files . Rusbridger discusses why NSA whistleblower Edward Snowden chose to approach the Guardian; the role of anonymity; and why issues of surveillance and information gathering are not being properly debated by the UK parliament.This conversation took place prior to a speech given by MI5 chief Andrew Parker at the Royal United Services Institute on Tuesday 8 October