How the Observer broke the story of NSA ‘dirty tricks’ at the UN in the runup to the Iraq war in 2003 will star Natalie Dormer as news source Katharine Gun

Harrison Ford and Anthony Hopkins have joined the cast of Official Secrets, the long-mooted film about the Observer’s reporting of the GCHQ bugging scandal in 2003, it has been announced.

In the latest film to cover the activities of whistleblowers and the journalists who report their revelations, Official Secrets will tell the story of Katharine Gun, an officer at the Cheltenham-based government eavesdropping agency. She leaked an email that contained a request by America’s NSA to illegally bug the United Nations offices of six key countries in the run-up to the UN’s vote on whether to authorise the Iraq war.

Gun’s revelations were reported in the Observer (the Guardian’s sister Sunday newspaper) by journalists Martin Bright and Ed Vulliamy, and Gun was arrested and charged with breaking the Official Secrets Act. However, her case was dropped in 2004 after no evidence was offered by the prosecution.

According to the Hollywood Reporter, Hopkins will play a retired general and Ford a veteran CIA agent. The have been cast alongside The Hunger Games’s Natalie Dormer, who will play Gun, and Paul Bettany as Bright. Martin Freeman plays the Observer’s foreign affairs editor – whose character name, Peter Edwards, appears to be a composite of Vulliamy and real-life editor Peter Beaumont, who is now the Guardian’s Jerusalem correspondent.

Official Secrets will be directed by Mandela: Long Walk to Freedom’s Justin Chadwick, and shooting is due to start in May.