“When I listened to the testimony, I realised this was something you could never learn, you can only feel and hear it.”

Shutting herself away in the viewing room, director Claire Ferguson spent a magnitude of hours intensely watching first-hand accounts of 12 Holocaust survivors, filmed over an incredible 14 years.

She had been approached by producer Llion Roberts to compile their stories, as well as an exclusive interview with Mietek Pemper, Oskar Schindler’s right-hand man,  into a compelling narrative of the Holocaust, the result of which is Destination Unknown, released in cinemas tomorrow.

More than a decade ago, Roberts visited Auschwitz-Birkenau, where he was moved by a photograph that reminded him of his daughter. When he later spoke of the experience with the son of a Holocaust survivor, he was motivated to find others and film their testimonies.

In the 400 hours of film he captured, Roberts discovered that some survivors had only begun talking in recent years. Some had never spoken at all, and for some, who have passed away since the making of the film, it would be their last opportunity to open up about a life marked by genocide.

“To have these testimonies and to be involved in this project was an absolute honour,” says Ferguson, who has previously worked on Aileen: The Life and Death of a Serial Killer, The End of the Line and Concert for George. “The survivors shared these stories, which are very personal and intimate. It was not something I could walk away from, I was compelled to do it and knew it was so important those voices were heard.”

She was particularly struck by the unique stories emanating from a “breadth of experiences”, from those who witnessed horrific brutality in the camps, to those who escaped, were kept in hiding or became partisan fighters.

For Ed Mosberg, who was liberated from Mauthausen, the physical pain he suffered at the hands of the Nazis still leaves an emotional scar more than 70 years later.

“You see this whip,” he passionately tells the crowd gathered at the Austrian concentration camp, clad in a striped uniform worn by inmates. “I was beaten by four men with this whip. I wished at that time I were dead, because those who are dead cannot feel it. I feel this, I feel this today. I never forgot this.”

Fellow Mauthausen inmate Marsha Kreuzman, reveals she too is haunted by the unspeakable horrors of her wartime experience.

She explains: “I could forget what I had for breakfast this morning, but I will never forget what happened for the five-and-a-half years in the concentration camp.

“Who was better off? The one who dies early in the war, or the one who suffers so much for so many years? If you think I don’t suffer now you’re wrong. I don’t sleep at night.

“I walked on snow and I was thinking I was walking on the stones. I was walking on dead people, on their bones.”

Helen Sternlicht, who is one of the 1,200 Jews rescued by Oskar Schindler, vividly recalls the sadistic brutality she witnessed at the hands of Amon Goeth, commandant of Kraków-Płaszów concentration camp where she was interned.

Speaking about the Jewish inmate she saw being “ripped apart” by one of Goeth’s savage dogs, Sternlicht said: “This scene is something that still causes so much horror in me”.

“I walked on snow and I was thinking I was walking on the stones. I was walking on dead people, on their bones.”

There were however those who witnessed great kindness in the face of such horror.

Eli Zborowski survived the war thanks to the bravery of Maria and Josef Placzek, who built a hiding place inside their home for his family.

“These people are angels, not human beings,” he reflects. “If it wouldn’t have been for them, you would think there is no humanity at all, that people are beasts for what they are doing to Jews.”

For Ferguson, their powerful testimonies reveal not just the facts of what happened, but how they have since moved forward with their lives.

“On the surface, many have gone on to marry, have children and build successful careers. But the emotional impact of their experience and their sense of guilt at having survived is all too apparent.

“You feel that survival guilt,” adds Ferguson.  “One of the things this film gives us is a sense of living pain. It’s not discussed or analysed, but you feel it in front of you.”

The director also noted how some survivors openly talked to the camera, in a way they felt they couldn’t with their own families – and sometimes to their own detriment.

Speaking on film, Stanley Glogover says: “I never spoke about it in the house, I never spoke about it before because it was too painful to tell anyone you loved. Then the children were born, they grew up and never knew anything what happened to me.

“Unfortunately, as much as I was hiding it from them, in later years I was very emotional, bringing back these bad memories.”

Ultimately the film shows they are all survivors, not just of Nazi persecution, but of life itself.

“Eddie Weinstein says of his two children and seven grandchildren that they are his answer to the final solution,” concludes Ferguson. “The pain will never go away, but they have managed to move on and live with that pain. Their sense of hope in the face of all this is extraordinary and humbling.”

Destination Unknown (12A) is in cinemas now. destinationunknownmovie.com