In an Earl's Court apartment block hallway, Natalie Dormer gestures for me to sit down. “Get yourself over to the stairs,” she smiles, “the red Hitchcockian stairs.”

The film she is shooting is In Darkness, a contemporary thriller – as if her nod to Hitchcock hadn’t already given that away – about a pianist named Sofia. Played by Dormer, the visually impaired Sofia gets entangled in a murder case when her upstairs neighbour is killed.

Today’s scene sees Dormer fumbling her way into the building’s lift, white cane in hand, with the creepy Marc (played by Ed Skrein) – who may or may not be the killer – in pursuit.

Dormer, the fiercely intelligent and striking-looking 36-year-old, who rose to fame on The Tudors and Game of Thrones, has spent days with people at the Royal National Institute for the Blind, getting “a crash course in visual impairment” to help perfect her character.

Natalie Dormer in 'In Darkness' (Vertical Entertainment)

Intriguingly, Dormer is also the co-writer of In Darkness, scripting it with the director – and her off-screen partner – Anthony Byrne.

“There was a drought of intelligent thrillers when we started writing this seven years ago,” she says, when we retire upstairs to chat, sitting at the dining room table on the set of Sofia’s apartment.

She cites films like Guillaume Canet’s Tell No One and Christopher Nolan’s Insomnia remake as rarities in the field. “And then when Denis Villeneuve popped up and did Prisoners, we were like ‘Exactly!’”

With a cast that also includes Joely Richardson and Emily Ratajkowski, Dormer is keen for the film to paint the nation’s capital in authentic brush strokes. “I get frustrated about not seeing the real London on camera. You either see candy box London, if it’s a [Richard] Curtis movie, or you see rough estate gangster [films]… you don’t see central cosmopolitan middle-class London, which is textured.”

'In Darkness'

For Dormer, creating her own script is a first – well, since her days at the Webber Douglas Academy of Dramatic Art. “Like most drama students I wrote a play while I was at drama school and thought I could write,” she says.

Then her acting career took off: playing Margaery Tyrell in Game of Thrones, working for Ron Howard (in Rush) and Ridley Scott (in The Counsellor) and featuring in The Hunger Games franchise.

The script for In Darkness began with Byrne, who wanted to create a story about a woman who hears a murder. On holiday, over dinner, he and Dormer started brainstorming ideas.

“I was trying to help him,” she says. “Then he said to me, ‘Why don’t you write it with me?’”

The idea had never occurred to Dormer, but it made perfect sense; despite all her success, she was not happy.

“I was frustrated about the quality of roles,” she admits. This was long before the increased calls for more diversity in film that have dominated the industry in the past couple of years, and seen films like Ocean’s 8 fire up the box office.

Co-writing her own script – and even answering questions on set from her co-stars – has been a real revelation. “It is really liberating,” she says.

Nevertheless, Dormer is wary of bandwagon-jumping, particularly with the clichéd call for ‘strong women’ in scripts.

Natalie Dormer as Margaery Tyrell in 'Game of Thrones' (HBO)

“I’m not a fan of the word ‘strong’. I think it’s very reductive. Let’s not just swing the other way… we want three dimensional anti-heroic women, the way we have anti-heroic men, since Humphrey Bogart, and Clint Eastwood.”

It’s an intelligent and rational view, and Dormer makes the argument persuasively. “I’m talking about gender parity in roles. I’m talking about the 50/50 movement. Let’s not swing the pendulum so far the other way. European cinema is famous for its three-dimensional female characters. It’s just that America and Britain are now catching up.”

Dormer’s work on In Darkness also came before she scored the role in the upcoming BBC co-production of Picnic at Hanging Rock, based on the novel by Joan Lindsay (and already a famous 1975 film by Peter Weir).

In the six-part show, set in the early 1900s, Dormer plays Hester Appleyard, the widowed headmistress of a school for young ladies; mysteriously, three pupils and a teacher disappear on Valentine’s Day – an event that impacts upon the whole community.

She characterises both Picnic’s Hester and In Darkness’ Sofia as similarly flawed. “[Sofia] is the same as Hester Appleyard: she is a scared human being, who is trying to work through her demons determinedly.”

Hester, meanwhile, is anything but strong. She may be fiery and determined, but she's also profoundly damaged - and in flight: “I actually think Hester Appleyard is someone who is running away.”

In corsets... Natalie Dormer in 'The Scandalous Lady W' alongside Aneurin Barnard and Richard Worsley in 2015 (BBC/Laurence Cendrovitz/wall to wall productions ltd)

Initially, she was reluctant to take on the role. “I didn’t want to get back in a corset. I’ve done a lot of work, but I’m primarily known – especially in the States – for corset-orientated work. [But] I’ve gotten in a corset no more than Keira Knightley has, or Kate Winslet or anyone else.”

Still, the image sticks – perhaps because, even before Thrones, Dormer made her breakthrough playing Anne Boleyn in The Tudors (shooting in Dublin, it was where she met Byrne) and then went on to BBC drama The Scandalous Lady W.

Gradually, she realised this “re-imagining” of Picnic At Hanging Rock wasn’t simply your typical period drama. “[I understood] that it was dark, that it was surreal, that it was a psychological thriller. And that it was funny. It was a plethora of things; it really had a high bar and it was ambitious.”

After a two-hour FaceTime chat with Larysa Kondracki, the director behind the first three episodes, she was hooked. “I went, ‘bloody hell, I’m going to Australia.’”

Exotic trips to far-flung places are something she’s used to, however. While Dormer describes her own upbringing, just outside of Reading, as “fairly conventional”, she travelled with the school’s public-speaking team to Botswana and Canada. Something of a high-achiever at school – she was also head girl and vice captain of the netball team – the only thing she couldn’t admit to was her desire to be an actress.

“In my heart I knew, but I didn’t say it out loud.”

Dormer was “academically strong” and won a place at Cambridge to read history, but then she didn’t get the A-level history grade she needed.

“S**t happens,” she laughs. “My path suddenly got changed on a dime, really. It got flipped around.” She went to London with her boyfriend – “my first love” – who was studying psychology at UCL, and spent a “soul-destroying year” doing temp jobs, from bar work to selling loyalty cards in a department store, as she tried to get into drama school.

Eventually, she made it. “It’s like anything in life,” she says. “[You need] perseverance.”

The same could be said for getting In Darkness financed. But since then, she’s also returned to pure acting roles, filming with Sean Penn and Mel Gibson on The Professor and the Madman, a tale about the compilation of the Oxford English Dictionary.

How was that? “We’ll have to save that for another day! When it gets released… there’s a bit of politics. When it’s cut, then we shall talk.”

It's certainly an intriguing response, but she won't say more – except to add that she took the role for exactly the same reason as she wrote In Darkness: once again, she was attracted to “a three-dimensional, troubled, and foibled woman.”