Sigmund Freud, the father of psychoanalysis, was saved from Hitler’s persecution of the Jews by a long-standing Nazi who was fascinated with his work, a new book reveals.

The fate of Freud and his family in Vienna hung in the balance after Hitler’s forces took over Austria in 1938. The psychoanalyst was first protected, then helped to escape to Britain, by Anton Sauerwald, a Nazi who had been put in charge of his assets.

In twists of Freudian complexity, Sauerwald was put on trial after the second world war accused of plundering the Freud family wealth — only to be saved after the intervention of one of Freud’s daughters.

The full story has emerged thanks to research by David Cohen, author of The Escape of Sigmund Freud, published by JR Books.

By the 1930s Freud was famous in Europe and the United States for his pioneering work on the unconscious. He had founded the International Psychoanalytical Association with Carl Jung and helped to start a publishing business.

His success had brought financial rewards and the family lived comfortably in Vienna. However, the Nazis ordered all Jews to declare their wealth and asserted that “all Jewish assets are assumed to have been improperly acquired”.

“Kommissars” were appointed to oversee the process. Sauerwald dealt with Freud. According to Cohen, he controlled not only the family assets, “but in effect their destiny”.

Luckily, he was no ordinary Nazi. Although he had made bombs for the Nazi movement, he had also studied medicine, chemistry and law. At the University of Vienna he had been a student of Professor Josef Herzig, who often visited Freud to play cards.

That friendship seems to have influenced Sauerwald but so, too, did Freud’s writings. “The books had an extraordinary impact on him,” Cohen writes, “an impact Sauerwald knew he must not let his Nazi superiors suspect.”

It was a dangerous line to tread. While Sauerwald used to knock politely on Freud’s door, the SS barged in. At one point SS troops hauled off Anna Freud, one of Sigmund’s daughters, for interrogation.

Cohen reveals: “Sauerwald did not disclose to his superiors that Freud had many secret bank accounts abroad. Instead, he took the evidence back to his own apartment, where he had a panzerkassette, a locked box for documents.”

As tensions grew and war loomed, Freud decided to flee. To do so he needed an exit visa. For that he relied on Sauerwald.

The Nazis wanted all the books of his publishing business to be destroyed. “Sauerwald did not want to see the books destroyed,” Cohen writes. “They were the root documents of psychoanalysis.” Instead, Sauerwald and an accomplice smuggled them to the Austrian national library, where they were hidden.

Dismayed by an order to turn Freud’s home into an institute for the study of Aryan superiority, Sauerwald signed Freud’s exit visa. He also helped to raise money; in June 1938 Freud left Vienna on the Orient Express.

Freud settled in London, telling one newspaper “all my money and property in Vienna is gone” — without mentioning his accounts elsewhere. In September 1939 he died of cancer.

After the war suspicions arose that Sauerwald had made off with the family wealth. Harry Freud, a nephew of Sigmund and an officer in the US army, had Sauerwald arrested and put on trial.

Sauerwald’s wife wrote to Anna Freud in London begging her to explain what Sauerwald had done. Anna replied: “There was not any doubt that your husband used his office as our appointed commissar in such a manner as to protect my father.”

She also wrote to Harry Freud: “[The] truth is that we really owe our lives and our freedom to [Sauerwald]. Without him we would never have got away.” Sauerwald was released and lived until 1970.

Cohen said: “There are three main reasons why Sauerwald was so keen to help Freud. He had been the devoted student of a man who had been very close friends with Freud. He understood just how important a man Freud was academically and, finally, I think a little bit of money may have changed hands down the line.”

This weekend David Freud, the Tory peer and great-grandson of Sigmund, said: “I didn’t know about this until I read the book. It was a pretty ambiguous relationship. But I think it rings true that he helped Sigmund in the way suggested.”

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