The film is due to be released later this year (Picture: Entertainment One).
A trailer has been released for 'Official Secrets' - a film telling the story of a political whistleblower during the Iraq war.
The political drama sees Keira Knightley play Government Communications Headquarters (GCHQ) translator Katharine Gun, who in 2003 leaked a classified email that urged spying on members of the UN Security Council to push the Iraq war, putting her life on the line.
The trailer for the film, directed by Eye In The Sky filmmaker Gavin Hood, sees Knightley joined by a British cast including Ralph Fiennes, Matt Smith and Matthew Goode.
In one snippet in the film trailer, Knightley's character responds to claims that she is a spy working for the British Government.
She says: "No, I work for the British people; I do not collect information so that the Government can lie to the British people."
She is seen becoming infuriated with Tony Blair, who is shown through old news clips, before discovering an email by a US National Security Agency official.
Gun put her life and career on the line to leak the email, which called for British help to bug the homes and offices in New York belonging to United Nations diplomats from six countries whose support over the invasion of Iraq would be vital.
The email became front page news on a national newspaper, and Gun was charged with breaking the Official Secrets Act before the case was later dropped.
The film follows the story as Gun and her lawyers set out to defend her actions.
Smith and Goode play journalists and Fiennes portrays Ben Emmerson, Gun's legal representation.
Official Secrets, which premiered at the Sundance Film Festival in January, is set for release in UK cinemas on 18 October.