“I work for the British people,” she says, and changes the course of the film – and history – forever.

Here, we speak to Gun about her real life-role as a whistle-blower, and what it’s been like seeing herself portrayed in a movie by Hollywood’s Knightley.

“When I saw that email it was literally like a red flag to a bull,” Gun tells Stylist’s Chloe Gray. “I had already researched Iraq, and I’d come to the conclusion that there was no justification for the war. I just instinctively reacted to it and I wanted to stop harm to others. I guess the whole issue politicised me.”

For a quiet woman from Cheltenham, the Official Secrets movie marks the second time she has fallen into the spotlight – albeit a more pleasant one. The first time she made headlines was in 2004, when the media barraged her for the leak after she was charged with breaking the Official Secrets Act.

“Ironically, becoming known publicly was my biggest fear. And it was partly because I’m on the whole a fairly shy person. And my marriage to my husband was very new at that juncture, and he had a very unstable status in the UK. So I really didn’t want any of that to be scrutinized because it just felt too vulnerable,” she says.

Gun was followed, denied legal advice and her Turkish husband faced deportation. She wasn’t charged for eight months – a gruelling period which is depicted as just a few unbearable minutes in the film. So how did she handle nearly a year of despair?

“You just have to get on with life, there’s no alternative,” Gun says. “You could curl up in a ball on your bed, but that’s not going to achieve anything. And of course there were days I felt like doing that and maybe did do that. But you do just get up and go through the motions and try and make that day count for something.”

Official Secrets exclusive: Whistleblower Katherine Gun reveals true story behind Keira Knightley’s new film