“Official Secrets” tells the story of whistleblower Katharine Gun (Keira Knightley), a British intelligence worker who leaked a damning memo in 2003, risking not only her job, but her freedom.

The memo, asking the U.K. to comply in the potential blackmail of five United Nations members in order to drum up support for the United States’ invasion of Iraq, was entrusted to reporter Martin Bright of The Observer.

“We did feel that we were being lied to. And we were lied to,” said Bright, who visited The City in April to promote the movie, which is based on a book by Marcia and Thomas Mitchell, with Gun and director Gavin Hood.

“There’s a sense that those politicians at the time knew what the truth was, and they knew what the lie was and they chose to go down a particular track,” Bright says.

“The only people who have been punished are the ones who tried to show what was really going on,” says Gun, who calls herself a third culture kid — having been born to British parents living in Taiwan — and consequently identifying with neither place.

Mentioning that third culture kids are considered to be highly empathetic, she says, “So that’s possibly one of the reasons it was me rather than somebody else.”

Hood, who won an Oscar for 2005’s “Tsotsi” and made “X-Men Origins: Wolverine,” “Ender’s Game” and “Eye in the Sky,” says that situation is what he loved about the story: “The film asks the simple question: What would you do?”

In his view, Gun’s occupation made her incapable of going along with the memo. As a person who speaks fluent Mandarin, she’s extremely familiar with Chinese culture. So when the government asked her to use her multiculturalism to understand what another country is thinking, and yet identify only with one country, it was a conundrum.

“I think it’s a glorious contradiction, one that I’m rather glad exists,” says Hood, who was born in South Africa.

While Hood calls her brave, Gun insists she’s not a hero. She couldn’t even make the connection while watching the film: “I know my own flaws only too well,” she says.

Though she felt intimidated upon first meeting Knightley, who wanted to deeply research her role, they instantly bonded over the subject of motherhood.

“It’s really daunting to meet such a well-known celebrity, but she was really approachable and really friendly. I was won over straightaway,” says Gun.

At the time of the story, Gun was 28, blonde with blue eyes; Knightley has light brunette hair and brown eyes.

Hood says he wrestled with the problem of whether to dye Knightley’s hair and use contact lenses, and that Knightley said she wanted to keep her real color.

Considering certain portrayals — Meryl Streep in “The Iron Lady,” Helen Mirren in “The Queen” and Christian Bale in “Vice” — Hood says, “In those situations, you as an actor are doing your utmost to perfectly impersonate this individual. It’s very different from what actors are generally called upon in fictional roles.”

On the other hand, noting that contact lenses “dull” and lose the nuance of eyes, he said he wanted to see Knightley at her most vulnerable: “So we stripped it down,” he says, to work from empathy, rather than impersonation.

IF YOU GO

Official Secrets

Starring: Keira Knightley, Adam Bakri, Ralph Fiennes, Matt Smith

Written by: Gregory Bernstein, Sara Bernstein, Gavin Hood

Directed by: Gavin Hood

Rated: R

Running time: 1 hour, 52 minutes