Based on real-life events, Official Secrets sees Keira Knightley return to the big screen as a whistleblower who exposed secret information about the run-up to the Iraq war. Here, she tells Georgia Humphreys more about the political thriller

Keira Knightley is discussing something “horrific” that happens as we grow up.

Most of us have a moment, even if on a small scale, where “you realise that ‘good/bad thing’, that you’ve been taught as a child, isn’t the way the world works”.

“It’s much more complicated. And the results for you, if you are somebody who decides to be a truth teller, can be pretty catastrophic,” continues the Teddington-born star, 34, referring to whistleblower Katharine Gun, who she portrays in new docudrama Official Secrets.

“It’s a funny thing when you actually go, ‘That’s the world we live in’. It takes all the innocence away.”

As politicians in Britain and the US angled to invade Iraq back in 2003, GCHQ translator Gun decides to leak a classified e-mail that urged spying on members of the UN Security Council to force through the resolution to go to war.

The film shows how, instead of being applauded for outing the truth, she was charged with breaking the Official Secrets Act.

Her life, liberty and marriage were at risk, but she had to stand up for what she believed in.

Gun told her story to authors Marcia and Thomas Mitchell, who, in 2008, published The Spy Who Tried to Stop a War: Katharine Gun and the Secret Plot to Sanction the Iraq Invasion.

After various attempts to turn the book into a film, it’s finally been brought to life in Official Secrets, which was penned by husband-and-wife team Gregory and Sara Bernstein, and directed by Gavin Hood.

For Knightley, who has previously expressed her interest in playing angry women, she saw a “righteous rage” in Gun.

“There’s anger, and of course there’s regret as well perhaps, because your entire life explodes, and what for? You didn’t stop the war,” suggests the two-time Oscar nominee, known for films such as Pride and Prejudice, Atonement and Bend it like Beckham.

“And yet, she was right. I loved all of those things within it – it really makes you question, ‘Would I have done the same? Would I be brave enough? Would I do right to do the same? Or would I just do what I was told?’

“And I don’t know what the answer to that is, but I find all of the answers to those questions really interesting.”

Knightley agrees it’s also interesting that Gun isn’t more famous.

But, she notes, the leak “was like a week before the actual invasion happened, so I think it got swallowed up with the actual war itself”.

The actress, who was 18 and shooting the first Pirates of the Caribbean at the time, admits she doesn’t remember it happening at all.

“I was surprised at myself for not, but then I realised I was actually in America and, course, as you see in the film, it didn’t really get reported in America.

“But that’s kind of why I really wanted to make this film; obviously that conflict hasn’t necessarily had a resolution yet, and we’re still sort of living in the repercussions of it.

“And yet this was a piece of that jigsaw puzzle, that lead up to the 2003 invasion, that I didn’t know.

“So, I thought it’s really interesting when you take something that is so much a part of people’s lives and understanding the world, and yet there’s this piece that has in some ways been forgotten.

“So, yeah, I felt like it was an important story to tell.”

The red-carpet premiere of Official Secrets was Knightley’s first public appearance since giving birth to her second child, with husband, musician James Righton, less than two months ago.

The pair, who married in 2013, also share four-year-old daughter, Edie.

As well as becoming a mum for the second time, it’s been an exciting year career-wise for Knightley, including her star turn as a French literary icon in Colette.

There was also her emotional role in The Aftermath; she played a bereaved mother who arrives in the ruins of Hamburg following the Second World War to be reunited with her husband.

Both were captivating performances, solidifying her versatility on the silver screen.

When it came to embodying Gun, how much time did she spend thinking about the morality of the character?

“I think as an audience member that’s what you do, definitely – and that’s the point of it.

“But I think in playing Katharine my job was to entirely tell the story from her point of view, and therefore I didn’t look, in the telling of it, to question it too much from different angles.”

She shares she “was lucky enough” to meet Gun for lunch and hear about her experience first-hand.

“Her point of view about it was very clear, and I think that’s kind of what I’ve tried to do. But, 100%, I think the joy of any of these films as an audience is to question, ‘Is she right? Is she wrong? What would I have done?’ I think that is the fun of these films.”

And the star continues thoughtfully: “The fun, and the important thing, because of that question, ‘How much do we want our secret services to be morally accountable for their actions? How much is that possible? Should people be whistleblowing? Should that information come out?’”

l Official Secrets is in cinemas from tomorrow.