When Sally Noach, a cigar-smoking Dutch refugee and carpet salesman, arrived in Britain in the middle of the second world war, British intelligence officers doubted his claim to have secured the release of hundreds of imprisoned Jews in southern France.

Now, almost 40 years after his death, his daughter, Lady Irene Hatter, has proved the truth of his story and also tracked down some of the estimated 600 people he saved.

Working with the researchers behind a new documentary film, Forgotten Soldier, Hatter, who lives in Hampstead, London, has solved some of the mysteries that had puzzled her throughout her adult life.

“There were always rumours that my father had been a spy and was interrogated by MI5,” she said. Others suggested he once ran the black market in Lyon, where he had profiteered like “a Jewish Harry Lime”.

Hatter remembers her father as a joker, with a fund of entertaining stories. Yet during her Amsterdam childhood, Noach had always refused to talk about the war, in which his parents and many other family members were killed at Auschwitz.

A box of memorabilia discovered three years ago by Hatter and her brother Jacques included thank-you letters sent to Noach by grateful survivors from places as far-flung as Jamaica, Suriname and Lisbon.

Among those Hatter has since tracked down are the descendants of Mimi and Barend Boers, a couple who married in Friesland, northern Holland, in the spring of 1939. Three years ago a seven-minute home movie found by their children was a viral hit on the internet. Many of the guests shown innocently celebrating were shortly afterwards persecuted and killed. But the bride and groom survived, thanks to Noach.

The heroic exploits of Noach, who was born in the Dutch city of Zutphen, began in earnest in 1940 when he travelled by train to Lyon in France. Once there, under the cover of working as an interpreter for the Dutch Consul, he repeatedly walked into prisons, hostels, factories and police stations demanding the release of people he claimed were Dutch nationals. He would forge “safe passage” papers for anyone he could – once filling in and stamping hundreds of documents at one sitting.

In 1942 Noach escaped France, leaving behind Maurice Jacquet, the official at the Dutch Consulate who had aided and supported much of his impromptu rescue work. Two or three months later Klaus Barbie, the Butcher of Lyon, arrived in the city and oversaw the deportation of many more Jews, including Jacquet, to death camps.

Paul Goldin, producer of the documentary, said: “The particularly sad thing is that Noach was then ostracised by many in the Dutch community in London, and disbelieved by the British authorities. Like Noach, those involved often did not want to talk about the Jewish resistance, especially if they had not been able to protect their own family.”

Noach returned to Amsterdam in 1947, where Irene and her two brothers were born. The Dutch government recognised his achievements in 1969.

In the documentary, Robert Gildea, an Oxford professor and expert on the resistance, explains that much of the subversive Jewish action had concentrated on getting people out, rather than on violence. “People saw resistance as basically people sabotaging trains or taking pot shots at Germans. But Jewish resistance and Jewish rescue was a war within the war.”

You can see Forgotten Soldier at the JW3 cinema in Hampstead, London, from the 17th to 21st February 2019.