Game of Thrones stars Indira Varma and Conleth Hill and Episodes’ Tamsin Greig have joined the cast of Gavin Hood’s spy thriller Official Secrets, which kicked off production this week.

The trio will join Kiera Knightley, Matt Smith, Ralph Fiennes and Matthew Goode in the thriller for Entertainment One (eOne), which tells the story of British intelligence whistle-blower, Katharine Gunn.

Palestinian-Israeli actor Adam Bakri, who starred in Oscar-nominated feature Omar, Swedish actor Myanna Buring, who has starred in the Twilight franchise and Downton Abbey and John Hefferman, who played Lord Altrincham in The Crown and starred as Major Harold Webb in Hood’s previous film Eye In The Sky, round out the cast.

Principal photography kicked off earlier this week in the village of Boston Spa, outside of Leeds. Hood has written and is directing with Ged Doherty (Eye in the Sky) producing with Elizabeth Fowler (Devil’s Knot) and Melissa Shiyu Zuo and Claudia Bluemhuber, Anne Sheehan, Hugo Heppell exec producing.

Hood said, “When I read Katharine Gun’s deeply personal story of conscience, I felt that a crucial missing piece of the “How we got into Iraq” puzzle had fallen into place. But more importantly, I was drawn to a simple yet profound and rather topical question which her struggle asks us to consider that is, if you discover that someone in power is doing something illegal or immoral, when do you, or would you, speak up? As with my last film, Eye in the Sky, my hope is that our audience will be engaged by a tense and emotionally satisfying story, and also leave the cinema with something to talk about after.”