This is the true story of GCHQ whistle-blower Katharine Gun (Keira Knightly) who leaked a 2003 memo detailing the US government’s plan to eavesdrop on UN Security Council members in the run-up to a crucial vote on the invasion of Iraq.

The likes of The Post and Spotlight have proved to be awards magnets in recent years by focusing on high profile leaks and newspaper investigations. And while Official Secrets is similar to those (as well as All The President’s Men and The Insider) it has the crucial difference of being a leak which had no effect on the course of history. This is unfortunate both for world events and the film, as its impact is diminished.

Because of this, the film focuses on Katharine, with the Observer investigation into the case for war shown through its effects on her legal position rather than geopolitics. Yet Katharine feels underdeveloped – her decision to leak comes before we’ve really got to know her – and isn’t helped by a one note performance from Knightly. The character is equally outraged throughout, including at the legal consequences of her self-confessed breach of the Official Secrets Act, making her look rather naive.

It has the superficial characteristics of cinematic tension like darkness and signposting music, but this is rarely reflected in the drama of the scenes, partly because we’re told she ends up on trial for leaking the document in Official Secrets‘ first act, and anyone who’s not been living in a cave knows the Iraq War went ahead (and even some people who lived in a cave, like Saddam Hussein).

It benefits from an all star cast which includes Ralph Fiennes, Matthew Goode, Rhys Ifans, Tamsin Greig and Matt Smith (who would make a great David Cameron), but this can’t make up for the film’s other flaws, which unfortunately leave it feeling like a waste of talent, with the brief few seconds of the real Katharine at the end more inspiring than anything in the previous two hours.