Family members of people kidnapped by Hamas have issued an emotional rallying cry for their release as a new exhibition opened depicting the conditions captives are held in.

British-Israeli Dr Ayalet Svatitzky, sister of Nadav Popplewell, said she had not grieved properly over the death of her other brother in Hamas attacks while Mr Popplewell remained captive.

Eylon Keshet, cousin of Yarden Bibas, who was abducted with his wife and two young children on October 7, called for all parties involved to agree on a “very basic moral page” to end the family’s “twisted and rotten nightmare”.

Both were speaking at the opening of the Voices from the Tunnels exhibition, as the time since the initial attacks by Hamas in Israel passed the 100-day mark.

Installed in a derelict basement space in east London, the exhibition displays what conditions are like in captivity based on the accounts of former hostages.

Former prime minster Liz Truss was among those who visited the exhibition on Monday.

Dr Svatitzky, 46, who lives in the Yagur Kibbutz in Israel, told the PA news agency: “It’s hard for us to believe that it’s already been 100 days. Never in a million years would I think that the hostages will be held so long by Hamas.”

Mr Popplewell, 51, has been a hostage in Gaza since October 7, but Dr Svatitzky’s mother Channah Peri, 79, was released as part of a temporary ceasefire in November.

Her other brother Roy, 53, was killed in the Hamas attacks.

She said: “On the one hand, I was very joyful and relieved that we’re going to get her back and I was able to hug her for the first time after 49 days.

“On the other hand, she didn’t know about Roy’s murder, so I had to tell her when she arrived at the hospital that she lost her eldest son.

“She hasn’t been able to mourn him yet, like I wasn’t able to mourn him, because our primary concern, our only concern, is Nadav and the other hostages that are still being held.”

Dr Svatitzky was told by her mother that hostages were only fed small portions of pitta bread and rice, and that Mr Popplewell had become very thin and depressed.

I ask each and every person with a conscience and a family to just call for their unconditional release, if they consider themselves human and compassionate

Speaking about her mother’s condition, Dr Svatitzky said: “As long as Nadav is still in captivity, she cannot recover.

“In a way she is still in the tunnels with him, so as long as he’s down there, there’s always this glass ceiling above her. We need him home in order for her to be OK.”

Mr Keshet, 30, told PA: “We need everyone here on the same page, on the human page, on the very basic moral page.

“I ask each and every person with a conscience and a family to just call for their unconditional release, if they consider themselves human and compassionate.”

Mr Bibas, 34, was captured with his wife Shiri, 32, and two children, Ariel, four, and baby Kfir, who was 10 months old when he was taken.

Mr Keshet said he believes the whole family is still alive, despite reports from Hamas that Shiri and the children had been killed.

Kfir will turn one on Thursday, and Mr Keshet said he would be “celebrating the saddest birthday in the world” with further calls for an immediate release.

He added: “We need everyone to help us bring them home now, because we don’t want to get them in body bags.”

The Voices from the Tunnels exhibition comprises multiple floors in a derelict building in an attempt to closely mimic the cold, damp conditions felt by actual hostages.

The first space resembles a hospital ward to emphasise that underground tunnels used by Hamas are hidden in plain sight, as well as a large mural of posters showing all Israelis still being held captive.

A series of underground rooms below depict the living conditions, medical treatment and physical and sexual abuse former hostages witnessed and experienced in Gaza.

Mannequins of hostages and Hamas soldiers are included in the rooms, while placards nailed to the walls explain the experiences of current and former hostages.

Orit Eyal-Fibeesh, co-founder of the 7/10 Human Chain Project who curated the exhibition, said: “This is the first attempt to really bring those stories to life so that we don’t forget and that we understand what’s really happening and what has happened.

“Bringing those families here is just another dimension of telling this story in the most reliable and accurate way.”

Ms Eyal-Fibeesh said Voices from the Tunnels was the first of its kind worldwide but that it represented “just a snapshot” of events in Gaza as many were too horrific to tell.

She said sharing the exhibition was important as remaining hostages were running out of time, adding: “People who came back after 50 days or 54 days were already in a terrible shape. Can you imagine twice as long?”