We could program an entire weekend film festival of Keira Knightley period piece films, from “Pride and Prejudice” to “Silk” to “Anna Karenina” to “The Duchess” to “Atonement” to “The Imitation Game” and of course all those “Pirates of the Caribbean” films which take place in some undefined part of fantasy history in which Johnny Depp has cornered the market on guyliner.

Knightley returns to the past again in “Official Secrets” — but it’s the recent past, i.e., the early 2000s, and she’s playing the real-life British intelligence specialist/translator who was put on trial for violating British law after going public with memos revealing the U.S. government was enlisting England’s help to blackmail United Nations Security Council members in order to coerce them to vote in favor of an invasion of Iraq.

Official Secrets: 2.5 out of 4 CST_ CST_ CST_ CST_ CST_ CST_ CST_ CST_ IFC Films presents a film directed by Gavin Hood and written by Hood, Sara Bernstein and Gregory Bernstein. Rated R (for language). Running time: 112 minutes. Opens Thursday at local theaters.

Unfortunately, while Gun’s story is certainly worth telling and this is a well-intentioned, solid film with fine work from Knightley, “Official Secrets” is too heavy-handed and drab, and falls far short of procedural thrillers such as “All the President’s Men” and “Spotlight” and “The Post” or broadly entertaining whistleblower stories such as “Erin Brockovich.”

In an early scene, Knightley’s Katharine Gun is watching a televised press appearance by President George W. Bush, who claims there are links between Saddam Hussein and Al-Qaeda.

“Come on, there are no credible links between Hussein and Al-Qaeda,” says Gun, adding, “Yes, yes, Saddam is a dictator, but he’s not a religious nut. Why would he risk arming Al-Qaeda? … It doesn’t make any sense!”

She might as well be addressing the camera directly, for all the subtlety of the scene.

We begin with a scene of Gun facing trial in 2004, and then get the obligatory “ONE YEAR EARLIER” title card taking us back to the beginning.

Working for the Government Communications Headquarters, Katharine comes across the aforementioned memo.

Katharine is not a traitor to her country. She loves her country. But she cannot stand silent with this knowledge. She leaks to the memo to an activist friend, and it eventually lands with Martin Bright (Matt Smith), a reporter at The Observer, which turns it into a blockbuster front page story.

“Official Secrets” is filled with standard-issue thriller sequences, with various characters surreptitiously meeting in parking garages (shades of Deep Throat!) and other out-of-the way places, with the score pounding home the ominous nature of these meetings and the cinematography favoring cool blues and grays. British thespian stalwarts keep popping up, from Matthew Goode and Rhys Ifans as journalists to Ralph Fiennes as Katharine’s lawyer.

We bounce back and forth from the journalists trying to ascertain whether the memo is real, or faked by some anti-war activist, and the parallel story of Katharine, who decides she must go public to confirm the authenticity of the memo.

Even when the screenplay provides one opportunity after another for Katharine to explode with righteous anger as she fights the charges, “Official Secrets” remains curiously ineffective in its efforts to win our full emotional investment. It’s difficult to become immersed in a film in which far too many characters sound like they’re reciting talking points and not delivering authentic dialogue.