NICOLE KIDMAN might have relinquished her anonymity 25 years ago, but she’s tried her hardest not to become cynical or jaded in the ensuing years.

“I’m still someone who wants to experience (new things). I have friends who say, ‘You know, I operate at about a four and I never want to go up to a nine, never want to go down to a one’. But I enjoy going up to a nine and jumping around and being incredibly excited – beyond excited – but that means I have to be willing to take the twos,” says the 47-year-old, who looks ten years younger with her thick mane of red hair in tousled waves and wearing a bohemian, floor-length dress.

And despite Kidman’s status in the upper echelons of movie stardom, she doesn’t want to become suspicious about people’s motives.

“I think for me, unfortunately or fortunately, I’m still incredibly trusting,” she adds. “That’s just the way I operate, but I choose to be that. I choose to stay very open to people, and I never go into something mistrustful.”

Born in Hawaii, Kidman moved to her parents’ native Australia as a toddler and trained as a ballet dancer, before edging into acting, landing her first film role aged 16. Worldwide recognition beckoned in 1989, following her performance in the thriller Dead Calm with Sam Neill, and three years later she married Tom Cruise – one of the most famous movie stars on the planet – after they met on the set of 1990s Days Of Thunder. The pair adopted two children, but parted in 2001.

Reflecting on her journey so far, Kidman, who now has two young daughters with country singer Keith Urban, whom she married in 2006, says: “There are times where you think, ‘Oh God, I would’ve loved not to have gone through that’, but in the same vein, you’ve got to go, ‘But that’s what’s made me who I am’.

“That’s what we try and teach our children, that life is full of contradictions, and the more we can navigate through the pain, the more we’ll understand when there’s joy. There’s no such thing as consistency.”

And the actress truly believes that.

“That’s when we get into trouble as human beings, trying to control things,” she asserts.

The question of whether we are the sum of our memories and experiences is one of the themes in her new thriller, Before I Go To Sleep.

Based on the bestselling novel by SJ Watson, the film follows Christine, a woman who wakes up every day remembering nothing, as a result of a traumatic incident in her past. And then one day, new terrifying truths emerge that force her to question everything, and everyone, around her.

“From the minute I read the script, it got under my skin,” says Kidman. “And the book itself has been such a huge hit, when I mention the film to people, they say, ‘Oh, I can’t wait to see it’.”

The movie marks the second occasion she’s worked with Colin Firth, who plays Ben, the husband she no longer recognises. “I get to play opposite one of the greatest actors in the world, so I’m always like, ‘Offer Colin everything’,” she says, laughing.

They starred together previously in last year’s The Railway Man, and were set to collaborate again in the upcoming big-screen adaptation of Paddington, until Firth dropped out, feeling his voice wasn’t right for the famous bear. The pair will reunite, however, to begin filming Genius later this month.

“I love working with Colin,” Kidman says fondly.

“He’s so easy, he’s extremely nuanced and yet he’s a listener. When you’re in a scene with him, he listens and responds; that’s the greatest acting.”

Oscar-winner Firth speaks highly of her in return.

“The way Nicole works is chasteningly authentic. I feel like I have to be at the top of my game. I can’t lie. I can’t be lazy about it. If I try to sell her a bill of goods in a scene and it’s not true, I’ll see it in her face. I’ll lose her.

I’ve got to convince her,” he says.

Kidman is known for her comprehensive research and character preparation, and confesses she took on the subject of amnesia with absolute commitment.

“Most of my research was to do with the condition, so that it was plausible, because if I can’t feel it and believe it, I’m hopeless,” she explains.

“In a film, I can’t stand it when there are big holes, and I can’t stand it when there’s uncertainty about whether it’s a real condition or a state of mind. I wanted to make sure that this was a real condition, so I watched a number of documentaries where people do have this psychogenic amnesia.”

The thought of suffering from it is “horrifying”, she says. “Someone described it as like losing their soul, because you lose your identity.

“You lose what you are and that’s really chilling, and also very sad.”

Kidman is no stranger to emotionally complex roles.

Challenging performances have included Ada Monroe in Cold Mountain and Virgina Woolf in The Hours, which earned her an Oscar and Bafta in 2003.

“At different times, I choose to throw myself into things which are probably extreme, but really, the reason I liked this movie was that there were some really great twists,” she says.

To help her navigate the complicated script, the director and screen-writer, Rowan Joffe, constructed a graph, to remind Kidman of Christine’s emotional state at any given point in the story. “It was helpful, because the story deals with time and fast-forwards and flashbacks. It was really complicated,” says the actress.

“I needed Rowan to track it, and it was a blessing he was the writer as well as the director.”

Her career may often be demanding and complex, but when she isn’t working, Kidman likes to keep away from drama, preferring to relax with her family in Nashville than hang out in Hollywood.

“I enjoy the great outdoors and Nashville has a slower, easier approach to life,” she says.

Despite her movie star status, she seems indifferent to the notion of celebrity; perhaps that’s why she can’t believe the recent furore over leaked naked images of a number of A-list stars (actresses Jennifer Lawrence and Kate Upton are among those reported to have had photos hacked).

“I work with the UN and women against violence, and there are so many things that are not publicised and should be focused on,” Kidman stresses. “Far more than the superfluous things.”

  • Before I Go To Sleep is in cinemas now

EXTRA TIME: BEHIND THE SCENES 

  • The book was written by SJ Watson, a former NHS audiologist who was inspired after spotting an obituary for an amnesia patient.
  • Director Rowan Joffe felt a personal connection to the story, as his mother had suffered amnesia following a brain haemorrhage a decade before.
  • The design team used a washed-out palette of greens and browns to portray the torpor in which Christine is living. Lighting was kept as natural as possible and Alfred Hitchcock’s eerie films Dial M For Murder and Spellbound used for inspiration.
  • Joffe used a hand-held camera to shoot many of the scenes, to make it “feel like it was a little kid holding Christine’s hand – and wherever she goes, we go, trying to work out if she’s happy or sad”.
  • Three weeks of interiors were filmed at Twickenham Studios, the exteriors of Christine’s house were shot in Surrey and scenes were also filmed in South London’s Greenwich Park.