Family history sometimes fails to turn up interesting stories. But the philosopher and writer Alain de Botton and his sister, the singer Miel de Botton, both members of a wealthy and cultured dynasty, must have suspected research into the life of their paternal grandmother would produce more exotic intrigue than anyone could handle.

Now the secrets of the clandestine life of Yolande Gabai de Botton, a spy known as the Jewish Mata Hari, are to be laid bare with the British premiere of a documentary film backed and produced by her granddaughter. “She had a great passion for her cause and she very much believed in the coexistence of Jews and Arabs,” said her granddaughter, Miel, this weekend. “I do feel there should be recognition for the way she neglected her own health and safety, and even that of her family, because of what she wanted to achieve.”

In Israel, the glamorous Gabai de Botton, who died in 1959, has a growing reputation as a key player in the foundation of the state after the second world war. Her charm, beauty and high-class international connections allowed her to travel undercover across the Middle East, often carrying secret documents at extreme personal risk. Only now, with the release of the film, is the impact of her unconventional lifestyle on politics and on her family becoming clear.

Gilbert de Botton, the late financier and father to Alain and Miel, will appear in the documentary, Yolande: An Unsung Heroine, when it is screened at Seret, the London Israeli Film and Television Festival, on Sunday [14 June] and he describes a childhood with a mother who was often absent and in danger. Her only son, he was sometimes left without enough food to survive when she was sent abroad on a mission. But he never blamed her, according to his daughter: “On the contrary. In fact, I worried that he was denying a resentment of her, because she was his idol,” she told the Observer. “He admired her endlessly and never said a bad word about her until the day he died.”

Born to a Turkish Jewish mother and raised in Egypt speaking French, Yolande was a favourite of King Farouk’s court and moved easily in Egyptian high society. At 17, she was married to a businessman named Jacques de Botton and her son was born a year later.

In 1945, when the head of the Jewish Agency’s political department, Moshe Sharett, visited Egypt, she was recruited as a secret agent for the Jewish settlement in Palestine at a cocktail party. A part-time journalist, she had access to editors at Al-Ahram, the most popular Egyptian daily newspaper, and among her admirers and sources of crucial intelligence were Tak ed-Din as-Sulh, chief assistant to Abdul Rahman Hassan Azzam – known as Azzam Pasha – and Mahmoud Mahlouf, son of the Grand Mufti of Cairo. The Swedish ambassador to Egypt, Widar Bagge, also fell under her spell and was persuaded of the Zionist cause.

“She died 10 years before I was born,” said Miel, who has Yolande as a middle name and is often told she bears a close resemblance to her grandmother. “We didn’t even see any pictures of her when we were children, so it was years before I understood what she did.”

Her brother Alain has described the emotional legacy of this “very spirited woman” and the effect on his late father. “He grew up in this very uncertain atmosphere. She was a single parent; they were Jews living in Egypt. There were times when he was looked after by the neighbours because his mother was in prison,” he said, adding that his father had found parenthood difficult because of his own “painful” experiences.

Among key documents Yolande supplied to the Haganah were the resolutions adopted by the Arab League in 1947 and 1948, declaring they would “sacrifice all the political and economic interests of the Arab world in order to save Arab Palestine”, and Arab military plans for the end of the British Mandate for Palestine.

In 1945, she was tasked with recruiting a network of Egyptian agents that included members of the Muslim Brotherhood and, in 1948, she flew to Palestine to pass David Ben-Gurion secret plans for Syria and Egypt to invade the new Israeli state. She had sewn them into her shoulder-pads.

Later that year, she was deported to Paris, but she continued to feed information back when she could. She returned to a small flat in Israel with Gilbert towards the end of her life, upset she had been forgotten by her former masters.

According to her late son, this marginalisation was one of two things that made her sad. The second was the death of an airman called Harmor she had married in the 1940s and whose name she kept.

SERET 2015 runs from 11 June to 21 June.