The sister of a UK national who remains hostage amid the conflict in the Middle East has warned “there is no more time” for those captured, and called for their release ahead of the 100th day since Hamas launched its attack on Israel.

Ayelet Svatitzky told the PA news agency she is hopeful for the release of her brother, Nadav Popplewell, but is fearful of how long he can hold on.

Mr Popplewell, 51, is one of two UK nationals who remain hostage – a figure announced by Foreign Secretary Lord David Cameron on Tuesday.

Mrs Svatitzky, 46, will be speaking at a rally on Sunday afternoon in central London calling for the release of all hostages, as Monday marks 100 days since Hamas’ attack on October 7 – the day “her life froze”.

The demonstration comes after thousands of pro-Palestinian protesters took to London, Dublin and Edinburgh streets on Saturday, calling for a permanent ceasefire in the conflict in which more than 23,800 Palestinians have been killed over the course of the Israeli response, according to the Hamas-run Health Ministry.

The protests, part of a global day of action involving 30 countries, came after the UK and US carried out airstrikes against Houthi bases in Yemen.

Mr Popplewell was captured alongside his 79-year-old mother, Channah Peri, both of whom are among an estimated 240 people originally taken prisoner.

Mrs Peri, released during the November ceasefire, was able to inform her family that her son had lost weight and had not been receiving medication for his diabetes, but the family have not heard anything about him since.

Mrs Svatitzky’s elder brother, Roi Popplewell, was found dead near his home just after the attacks.

He was 53 when he died, and the family marked what would have been his 54th birthday on Christmas Eve.

Mrs Svatitzky told PA how her mother has not been able to mourn his death because the family are consumed by their worry for her other brother.

“That’s all that’s on our minds all the time is Nadav’s wellbeing and his condition, and he’s in danger every second of every day,” she said.

Mrs Svatitzky, who lives in Kibbutz Yagur, said she still has hope.

“Hope is what gets us up in the morning,” she said.

“My biggest fear is, I don’t know how long it’s going to last, I don’t know how long he can hold on and I don’t know what his condition is.

“I’m hoping he is going to be released soon but like I said, I saw how my mum came back after 49 days, I’m very scared for how he’s going to come back.”

She will be calling for the release of all hostages at a rally in Trafalgar Square on Sunday afternoon.

“My main message is that the hostages are running out of time and that we should all do everything in our power to demand their release,” she told PA.

“I think this is the prime message: There is no more time.”

Mrs Svatitzky called it a “crime” that people remained hostages almost 100 days since October 7.

“There’s so little that me as a family member can do,” she told PA.

“We can only be a voice to our family members and our loved ones who are being held against their will for almost 100 days and demand their release, but there really is (only) so much we can do.”

Reflecting on the time that has passed, she said: “Our life froze October 7.

“This is all I do in my life – I help my mum in her rehabilitation process, and I fight for Nadav’s release.

“I don’t work. I’ve got three children. I call myself a present-absent parent, because I’m here in body but I’m not really here because my main focus and concern is saving my brother’s life.

“My life froze October 7, and I don’t know when I’m going to get it back.

“And I know that when we get Nadav back it’s going to be a really long road for recovery.

“When I look ahead into the future I don’t know what it’s going to look like. I can’t predict it.”

Mrs Svatitzky was alerted to attacks in Kibbutz Nirim – where her two brothers and mother lived – on October 7 by messages from a WhatsApp group she shares with childhood friends.

She told of how she phoned her mother and had a brief conversation with her before hearing men’s voices in the room.

“I realised that the Hamas terrorists got to her house”, she told PA. “They were speaking in English with an Arabic accent and I could hear that over the phone.

“So I hung up immediately because I was convinced that the next thing I’m going to hear is my mum being murdered.”

She next phoned Mr Popplewell before hearing the same voices seconds later.

She said she then received two pictures on WhatsApp from her mother’s phone – showing the elderly woman sitting in her living room “in her nightwear” beside her barefooted son, with a follow up message: “Hamas”.

Mrs Svatitzky said a third picture, one featuring “armed terrorists in the corner”, was uploaded to her mother’s Facebook story.

Mrs Svatitzky and Mr Popplewell are both UK nationals, and so was their third sibling, Roi.

Both brothers were single and had no children before the events of October 7.