An old school photo slides from the printer into Frank Bright’s hands. It is black and white because it dates from May 1942. But since it was taken, tiny red and blue stickers have been scattered over the image.

Red for dead; blue for survived. Most are red.

Bright, now 90, points to a younger version of himself, a tall lad in the back row. Some time after the photo was taken, he and his mother arrived at Auschwitz. She was immediately sent to the gas chambers; his father had already been killed at the camp.

Bright spent years researching the fate of his classmates, cataloguing them on a spreadsheet. Number 24: “She had ginger hair as far as I remember … sent to Auschwitz in October 1944, did not survive.” Number 9: “A very pretty girl – I think I had a crush on her but from a distance. Sent to Auschwitz, did not survive.”

In the BBC documentary The Last Survivors – to be broadcast on Holocaust Memorial Day, 27 January – Bright says: “I can’t really communicate with others properly because they don’t know what I’m talking about. I mean how many people in England have their parents murdered, or see a gas chamber in action? It has affected me, yes.”

He adds: “You’ve got to forget about it, you’ve got to wear blinkers.” If one got too emotionally involved, “I’d be sitting here crying my eyes out”.

The Last Survivors features a handful of people, now in their 80s and 90s, who were children when they experienced the horrors of the Holocaust and the Nazi death camps.

There is no central record of Holocaust survivors in the UK, and the exact number of those still alive is unknown. But these are among the last people who can provide first-hand testimony of what happened.

Arthur Cary, the documentary’s director, said: “It’s a film that will be very difficult to make in five or 10 years from now simply because there won’t be many survivors left, and those that are still here may not be in a position to engage in the same way.

“And even though the film is not overtly political, this is an important time to make a film like this. When we look at what’s going on in the world around us, whether it’s the rise of the far right, or continued genocide in Burma, it felt like an opportune moment.

“I think it was a comfort to these survivors to know that, after they were gone, the film would endure and there would be an opportunity for future generations to hear their testimonies.”

Some of those featured in The Last Survivors did not talk about their experiences for many decades, believing it was better for them and their children to move on.

Anita Lasker-Wallfisch, 93, who survived Auschwitz because she played the cello in the camp orchestra, says the Holocaust was “not family conversation … It doesn’t fit into normal life and I wanted to have a normal life”.

Ivor Perl, 86, who returns to the site of the Auschwitz camp for the first time in the documentary – a deeply painful visit, in the company of his daughter and granddaughter – said he had been reluctant to tell his children what had happened. “But running away from it wasn’t the right thing either.” He adds: “I’m crying in my heart every day.”

Many survivors simply wanted to get on with their lives after the Holocaust, said Cary. “But now they are thinking of the past more than they ever did before. Knowing they may only have a few more years to live, they are in a more reflective space.

“It’s very traumatic for them to go over the past, but they also feel a responsibility to do something with their status as survivors. And the world is looking to them more and more because we are conscious they won’t be with us much longer.”

The Last Survivors will be shown on BBC Two on Sunday 27 January at 9pm.