An index of Wild Swans' success might be to compare it with Delia Smith, say, whose Winter Collection has reached sales of about half a million.
Jung Chang herself, modest and soft-spoken, is pleased but not overwhelmed. Throughout the world, the book has sold around six million copies. Only in China, where the book is still banned, have readers not had a chance to react to this powerful story of three generations of women in the turbulent changes from feudal times to the Cultural Revolution.
"Although it is now possible in China to mention the Cultural Revolution," Jung Chang explains, "you are not supposed to analyse it or discuss details - that's too dangerous. And personal stories are certainly too explosive."
At the party this week, guests will have a chance to meet Mrs Xia Dehong, Jung Chang's mother, who at 65 still lives in the Chinese town of Chengdu. She speaks no English but her life has been transformed by Wild Swans. "My mother was a very anguished person before she had a chance to talk about what she has lived through," Jung Chang says. "Now she is happy and tranquil."
The story behind the story - of how the silent mother finally told her daughter about her life, and how the daughter made it into a best-selling book - has become well known. Jung Chang came to England on a rare scholarship in 1978, and in the early 1980s married Jon Haliday, a Far East specialist. She visited home, but not until 1988 could her mother visit London.
In the freer air of a foreign country, Xia Dehong began to talk. About her husband - "My father put the revolution first, and his family second," Jung Chang explains - and about the imprisonment, hardship and humiliation, torture and political disgrace she suffered. She told of the 1000-mile trek from Manchuria to Sichuan when her husband, a senior party member, was entitled to go by horse or jeep, but, fiercely idealistic, made no concessions to family. His stumbling, sick and pregnant wife was made to walk.
"In the Cultural Revolution it was dangerous to speak even to your children," Jung Chang says, "so my mother had told me nothing. I didn't understand so many things." Odd memories fell into place: she recalls when she was tiny being visited by her mother in a state nursery. When it was time for her mother to leave, she cried and clung to her, so her mother sat with her until almost midnight. Only 20 years later did she learn that her mother had been imprisoned in 1955, and was that day on parole that was up at midnight.
Jung Chang also heard tales of Yu-fang, her grandmother, who provides the book with an unforgettable opening sentence: "At the age of 15 my grandmother became the concubine of a warlord general ..." When she was two, her feet had been smashed and bound to a few inches in length, a disfigurement that gave her perpetual pain.
The family were part of the Communist official elite, and Jung had an excellent education.
But in 1966, the Cultural Revolution meant Jung's parents were scapegoated, tortured and sent to distant labour camps. Her father suffered a breakdown; her beloved grandmother fell ill and died. Of herself at 14, she has said: "There was never any question of not becoming a Red Guard. I was one of Mao's babies."
Three decades later, this one of Mao's babies is writing a biography of the Chinese leader, together with her husband. So, despite her comfortable life in Notting Hill Gate, London, and her fame, not to mention her presence in the lists of Britain's richest women, she is still deeply involved in her native country.
She hopes that the Mao book will be as accessible as Wild Swans. Well, you never know. Few would have predicted that a long, serious, often agonising family story by an unknown Chinese woman would make publishing history. But as Stuart Proffitt explains: "How the human spirit survives, when it has been put under extreme pressure for very long periods of time - that is what the book is about, and that is its enduring appeal."