I think of myself as fundamentally Jewish — but it has been a hell of a struggle, against a sense of illegitimacy, and that it’s a gift that has been bestowed on me, that I can never take for granted.”
Londoner Simon May is a philosopher, professor and the author of a number of books relating to that field. But his latest book, How To Be A Refugee, is a radical departure and, indeed, may set the bar even higher for wartime-related personal stories.

It is many things: a thriller, a detective story, a story of restitution. Above all May’s book is a search for identity, because of decisions taken by his mother and father’s families, to convert away from Judaism to Christian denominations. German Jews on both sides, his mother’s family suppressed their heritage to the point where, perhaps, they no longer believed that they had ever been Jewish.

The denial and not-quite-denial led to May’s mother, Marianne, a classical violinist, both converting to Catholicism, yet declaring that she would only marry another Jew. Which she did, albeit in church. May and his younger brother, Marius, were circumcised, at their mother’s insistence; yet Simon became an altar boy in the local Catholic church. Marius, who died last year, cut through the conflicting cultural influences much more clearly: he had a “late barmitzvah” aged 40, at the Kotel in Jerusalem, and made aliyah. He even, with his mother’s approval, played cello in the Jewish Youth Orchestra. “He was far too good for it but I think he wanted identification [with other young Jews].”

Simon May, for his part, has acquired a German passport, but has hovered on the edge of moving to Berlin for years. His book is a passionate and eloquent account of a lost world of German Jews, cosmopolitan, sophisticated and cultured — and, so often, assimilated.

This poisonous embrace — for, as we know, neither assimilation nor conversion saved many thousands of German and Austrian Jews — is meticulously unpicked by May, who took the opportunity to grill, ruthlessly, his mother Marianne and his two aunts, Ilse and Ursel, about their lives. Importantly, he did so from an early age as he tried to work out who he was — German? British? Jewish? Catholic?

It’s been an obviously painful and emotional voyage of discovery for May. “You know how,” he says, “when you hear a note of music, you never hear it just by itself, there are innumerable sub-texts and frequencies.” It’s the same with this story, he says: “overtones and undertones, which I absorbed, of the unfathomable suffering which this heritage caused my mother’s family”.

The irony, he says, is that he and his brother grew up in a community which was almost exclusively Jewish by heritage. His mother’s friends were writers and musicians, some of whom were later to become well-known names such as Norbert Brainin, of the Amadeus Quartet, or the cellist and survivor Anita Lasker-Wallfisch.

He reels off a list of famous Jews who converted to Christianity, from Karl Marx to Heinrich Heine and Gustav Mahler. But what happened in his mother’s family, the Liedtkes, was different, May says. “What happened to us was a far-reaching immolation of inherited memory, of cultural memory, of a sense of having this tremendous inheritance. Reclaiming that, when you are raised not to think of yourself as Jewish… my mother was the only one of the three sisters who did continue to think of herself as Jewish”.

To their credit, none of the three women appears to have held back in answering his questions. We learn of the genuine pained bewilderment of his maternal grandfather, lawyer Ernst Liedtke who, despite converting to Protestantism, was expelled from his profession as as early as April 1933, after the Nazi ban on non-Aryan lawyers. Ernst died in December that year,  a few short months after being thrown out of his own legal offices and subjected to foul abuse by his clerk. He died on his own doorstep, in his wife Emmy’s arms.

Thereafter the lives of the three sisters followed very different trajectories. Late last year and long after he finished the book, May was contacted by the head of a music archive in Berlin. “Are you the grandson of Ernst Liedtke?” Yes, said May. The curator had discovered a letter written by Ernst, in the last months before his death, imploring the violinist and teacher Max Rostal to take his daughter (Marianne, May’s mother) to England. “The letter was written after he had been thrown out of work, and it is so heartbreaking… he says to Rostal, you will understand (he meant as a fellow Jew), for those in my circumstances it has no longer become possible to afford anything. I’m asking to take my daughter to England and to teach her for nothing, because I can’t pay you”.

In fact, Marianne began spending several months at a time travelling between Berlin and London, from 1934 to 1938, studying with Rostal. But when in 1938 her German passport expired, she was unable to renew it without Aryan papers. Saying her parents were German was no longer enough. Marianne, to her great good fortune, was “stuck” in London, warned by an official at the German Embassy that if she should should return to Berlin without a valid passport — and the birth certificates of her parents and grandparents to achieve such a document — she would be transferred to “a special camp”.

What of the other sisters? Both survived the war in remarkable circumstances. Ilse, a photographer, had converted to Catholicism like Marianne and Ursel, after Hitler rose to power. Each described the move as “the most wonderful moment of their lives”, at least until they had children. Ilse told her nephew that she had lived through the Third Reich “as if she had nothing to fear. She didn’t go into hiding or take an assumed name. She didn’t try to get herself certified as Aryan, or marry into a new identity… on the contrary, Ilse continued to dwell with brazen normality at the heart of Hitler’s Berlin”.

Most remarkable of all, while continuing to party with high-ranking Nazis, Ilse had a double life, in which she helped to hide and feed Jews in Berlin. These were the so-called “submarines”, Jews who had ripped off their yellow stars and relied on a clandestine network of people to give them refuge. At great risk, Ilse was a member of this network, one of the leading members of which was Christabel Bielenberg, a celebrated heroine of the resistance to the Nazis.

Ilse, says her nephew, was “fascinating. She was very quiet but she talked about everything, the works, including her Nazi boyfriend.” But at no time did he gain the impression that Ilse was reclaiming her Jewish roots by rescuing Jews. He’s still unclear as to what made her do it.

Ursel, an actress, took a different route. She decided to register herself as an Aryan, a supremely risky thing to do because of the many ways a claim could be undermined. Ursel pretended that she was not the daughter of Ernst Liedtke, but the result of an adulterous fling by her “allegedly non-Jewish mother”. After a lot of back and forth and provision of false documents, Ursel succeeded. But she went further, marrying into the German aristocracy, persuading her husband to desert the Wehrmacht, and surviving the war years in hiding in Amsterdam.

On top of these terrifying adventures, Simon May tells some extraordinary stories, including the search for heirs of the Liedtke family in order to win the restitution of a commercial building in Berlin. Ursel flatly refused to have anything to do with the share-out. There is a Jew who becomes a Catholic priest, the attempt to trace the fate of a great-uncle who was murdered in the camps, and throughout it all the hard-headed pragmatism of May’s mother and her aunts. He also spent time tracking down the family of his father Walter, who died, ironically, in London’s German Embassy.

His mother, says May “could make my jaw drop” with her conflicting responses to Jewish identity. When Marius decided to have his late-life barmitzvah in Jerusalem, May flew from Tokyo, where he was working as a professor, while his mother came from London. “She said to Marius, your ancestors would be very proud of you. As the Americans say, go figure. She had put us through total agony… I felt so displaced and so out of place. After I was about 20, I never entered a church again: but I never did what my brother did.”

He’s not ruling it out, however, and recalls a meeting with the late Rabbi Sacks, a fellow philosopher. “He told me, the door is always open for a return”.

Intellectually, Simon May knows this. Emotionally, he’s not yet ready to step through the door. “The mystery, for me, is my internal mystery — why haven’t I yet gone the whole hog [and committed to Judaism]? What’s holding me back?” But in fact, he says:  “Fundamentally, I’m a very religious person. I wouldn’t be surprised if I became a very religious Jew, at some point. I have it in me.”

How To Be A Refugee, by Simon May, is published by Picador at £20