In 1997, Vicky Unwin answered her doorbell in Belsize Park to be greeted by a long lost cousin.

Helen had come to London from Canada for a gathering of Kindertransport survivors rescued by Hampstead stockbroker Sir Nicholas Winton. Not only had Vicky never heard of the Kindertransport, but she had no idea she was Jewish or that her relatives had perished in the Holocaust.

Her journey to discover why her "very British pipe-smoking father" concealed his origins led to the discovery of a half sister and a grandfather whose play was banned by Goebbels.

Ham & High: Tomas Ungar became Thomas Unwin when he moved to London from Prague and became the archetypal pipe smoking EnglishmanTomas Ungar became Thomas Unwin when he moved to London from Prague and became the archetypal pipe smoking Englishman (Image: Courtesy of Vicky Unwin)

But after travelling to Prague, Israel, and Thomas' hometown of Boskovice in Moravia, she was upset to realise that the charismatic father, who as a UN diplomat had advocated for refugees from Rwanda and Cambodia, had turned his back on his own family.

"As a child you become aware of your context," she says. "I knew my father was Czech so was interested in that but I had no idea I was Jewish. Even though he wasn't in a camp the effect of losing your family on Holocaust survivors is complicated so I started the book thinking this difficult, sometimes unpleasant person hid his past because he didn't want to think about it. It was only later that I had the courage to read his letters to my mother that I saw it differently. The Holocaust was part of it but what was really shocking was he wasn't a very nice man."

Tomas was born in Prague in 1923 to Czech Jewish writer Hermann Ungar. A friend of Brecht, Stefan Zweig and Thomas Mann, he died in 1929 of appendicitis and Tomas was sent to London in late 1938 to escape the Nazis. His mother and brother left Prague just before war broke out with forged papers and the family moved to Fairfax Road, Belsize Park when Tom was 16 and then to the West Country.

Vicky has painstakingly researched her lost family and discovered that Hermann's parents and brother were killed in Auschwitz.

"Cousin Helen got out on the last train. She was six, her sibling was four, they never saw their parents again. Her mental health was badly affected by what happened. In Canada she was farmed out to work for people who treated her badly and abused by a foster carer, but my father was unable to feel sorry for her."

Tom's affair with a married woman Joyce led to a daughter Bonnie, born in 1944. But he said nothing of this to Vicky's mum Sheila when he met her in 1945 as a WREN in Germany.

"He had bright blue eyes and a fair complexion, he looked very Czech and spoke 11 languages so it was easy to pass himself off as English. As time went on he became so worried about being found out he became the caricature of a pipe-smoking Englishman. He would make anti-Semitic jokes and jest that his nose wasn't Jewish. As with all narcissistic people he believed his own truth."

Ham & High: Vicky's grandfather Hermann Ungar was a close friend of Stefan Zweig and Thomas Mann whose play was once banned by GoebbelsVicky's grandfather Hermann Ungar was a close friend of Stefan Zweig and Thomas Mann whose play was once banned by Goebbels (Image: Courtesy Vicky Unwin)

"The epiphany was going into my father's study in my 30s, seeing pictures of my grandfather, and thinking I had never been told the truth. We were all a bit dim, you believe what your parents tell you until you get old and realise they have motives for not telling."

After a distinguished career in publishing, including editing four Nobel prize winners, it was a revelation that Vicky's grandfather was a renowned writer.

"I was astonished to find the suitcases with the first editions. Thomas Mann and Stefan Zweig thought he was a great writer but his legacy died the death and has been resuscitated in recent years. Hermann was a man ahead of his time, a tortured genius, but he wasn't nice to his wife and never saw his children."

In 2009, believing he was dying, her father confessed to the daughter he had abandoned. "I was completely shocked and furious and said 'how could you deceive everybody?' I insisted on a DNA test but just looking at the photograph, Bonnie was my spitting image and we got on like the proverbial house on fire."

Vicky discovered that Joyce was thrown out by her husband and "lived in abject poverty".

"He just ran away and ruined Joyce's life never acknowledging their child. Bonnie didn't even blame him for abandoning her, she just wanted was to be part of the family that had been denied to her for 60 years."

Ham & High: Vicky with her father Tom and mother Sheila in Zomba MalawiVicky with her father Tom and mother Sheila in Zomba Malawi (Image: Courtesy of Vicky Unwin)

Tom also kept Sheila short of money after their divorce, while Vicky visited him in exotic locations where "money flowed like water".

"He was only interested in himself and what he considered important. He had no empathy for his family who were refugees while busting a gut to save West Papuan refugees or dying Ugandans. It was all about being seen as a hero and the centre of attention. When I showed him my research he was disinterested in how many of his own family ended up in the gas chambers."

The book has helped Vicky to understand this complicated figure.

Ham & High: Vicky Unwin's The Boy from Boskovice is published by UnboundVicky Unwin's The Boy from Boskovice is published by Unbound (Image: Unbound Books)

"I understood why he could be so horrible to me at times and at others so wonderful and loving - the dad of my childhood. He would flit in and out of my life depending on what he wanted from me. I needed to write the book to have some peace. I still have nightmares worrying if I have betrayed my father's memory but I have relied on his own words in the letters to tell the story and my conscience is clear."