Even while defending the medium in his pamphlet Why Documentaries Matter, BBC Storyville editor Nick Fraser conceded such films regularly contained an ‘unacknowledged left-wing bias’. Yet increasingly, from box-office successes such as Fahrenheit 9/11 and Food Inc. through to the increasing influence of NGO-backed documentaries, filmmakers are more openly acknowledging that bias, producing opinionated and partial essays on topics arguably overlooked by traditional media outlets. Such films can undoubtedly make a considerable impact on wider debate, most notably around the environment (An Inconvenient Truth, Gasland), economics (Inside Job, The Corporation) and civil liberties (Taking Liberties, Erasing David). The much-discussed decline of the classic investigative documentary, once defined internationally by the likes of British series World In Action and Panorama, seems to have been reversed in cinemas and online.

Yet, for many, the controversy over the Kony2012 viral-video campaign highlighted the problems of when political passion lapses into propaganda. While the funding debate focuses attention on how to maintain editorial independence, the role of filmmaker as activist raises further difficult questions over what that independence means. Films which take a more critical, but no less partial, perspective on popular campaigning topics can face arguably more difficulties in attracting funding and securing an audience, as the controversies dogging films by more idiosyncratic directors such as Martin Durkin or Adam Curtis suggest. Furthermore, in the wake of numerous scandals over faked footage and the deliberate blurring of boundaries in art-house docs such as Catfish, there are sensitivities over how far filmmakers should be allowed the freedom to experiment or demonstrate creativity in the pursuit of truth.

Should documentaries aim to offer the audience a balanced, impartial view, or is there more need than ever for opinionated, even biased, filmmaking? What about complex issues which do not sit comfortably in a straightforward category, or require a fresh approach? When does activism lead itself in to sermonising or even propagandising? Is the campaigning documentary a continuation, or corruption of, a tradition stretching back to the early days of celluloid? To what extent can documentaries change the world?