The book has been hotly debated on bulletin boards and the publishers have received scores of letters of thanks. One, written on a postcard in an elderly person's hand, said simply: 'Please thank the author.'

The author ignores her notoriety, declining interviews with journalists from around the world. Released in 1979 after 10 years in jail, Zhang, 62, became an internationally recognised expert on traditional Chinese opera through her work at the China Art Research Academy. The most recent photograph of her in the book shows her in a Beijing apartment in the 1990s.

Her reticence stems partly from fears over the book ban, along with an old-fashioned Chinese intellectual distaste for self-publicity. Friends say Zhang believes everything she has to say is in the book. But her shyness also reflects the scars of decades of isolation that followed the humiliation of her father and his peers. Zhang writes in the preface to her book: 'I pick up a pen to write in order to find a reason, and the strength, to go on living.'

The editor Wang describes his reaction when he read the manuscript last year, after it was recommended to him by a friend. 'I've been an editor for 20 years and I had never seen anything like it,' Wang says. 'I burst into tears at home. My daughter was asking: 'Mummy, what's wrong with daddy.' My wife said: 'Shhh, daddy's busy. Leave him alone.' It was brilliantly written. And the suffering of the people. It was too much to bear.'

Lured into the open by Mao's promise in late 1956 of greater political freedom in the 'Hundred Flowers Movement' (the name derives from a typically Maoist blend of a folk description of spring: 'A hundred flowers bloom'; and a classical saying: 'A hundred schools of thought contend'), Zhang Bojun, his colleagues Luo Longji and Chu Anping, among many others, offered what they believed was constructive criticism of the Communist Party, which they saw as developing dangerously totalitarian tendencies. The communists should not be 'the only party under heaven', as they had appointed themselves. China badly needed a genuine parliamentary system and a separation of powers, the democrats argued.

But the Hundred Flowers was a trick. In the summer of 1957 Mao abruptly turned on the democrats. In a chilling precursor to the Cultural Revolution less than 10 years later, in 1966, Zhang, Luo and Chu were forced into self-criticism after self-criticism.

Against this backdrop of high politics, Wangshi powerfully personalises the protagonists. Zhang portrays them as sympathetic individuals who'd had families, loves and hates; who suffered and died in shame. Their foibles and indulgences are recorded, too. The book records how one member of the inner circle, Shi Liang, who denounced Zhang Bojun when the crackdown began and went on to have a successful career, was partial to a particular type of expensive silk called xiangyunsha. Shi also recommended changing washcloths every two weeks. To the teenager, this was the height of luxury. It's also part of a China that has long gone.

To this day, Zhang, Luo and Chu have not been politically rehabilitated, unlike many other victims of China's many violent campaigns. The reason for the continued lack of forgiveness? 'They called for a separation of powers and they repudiated the position of the Communist Party as the only party under heaven,' says a personal friend of Zhang's, who requested anonymity.

In two short months after its publication in Beijing in January, Wangshi sold 160,000 copies. Then in the early spring the Chinese government pulled the plug, giving the book the dubious honour of being one of two banned in a list circulated just prior to the annual National People's Congress in March (the other was An Investigation of China's Peasantry by Chen Guidi and Wu Chuntao). Mainland editors estimate about 200,000 pirated editions have been sold since then. 'Of course, for our publishing house it's a financial loss,' says Wang.

In Hong Kong, where the book is published by Oxford University Press under the title Zuihou de guizu (The Last Aristocrats), it has reportedly sold 23,000 copies, which is considered a high figure. A Taiwan edition is on the way.

Undeterred, Zhang Yihe, who lives modestly in Beijing, is still busy writing. Copies of her essays are posted online as soon as they are finished. One of her latest essays, a more detailed, personal account of her father, came online in late July. Wangshi has not been published in any foreign language as yet, though Zhang has been approached by several well-known translators.

Zhang suffered prodigiously from being the daughter of an 'arch-Rightist'. When the axe fell on her 1958, she writes, she immediately lost all her playmates. From then on she was a solitary child. Much worse was to come. In 1969, at the height of the Cultural Revolution, she was sentenced to 20 years' jail for having 'betrayed herself as a counter-revolutionary', after criticism of Jiang Qing, Mao's fourth wife and leader of the extremist Gang of Four, was found in her diary.

Released in 1978, two years after the Gang's fall from power, Zhang to this day cannot abide the rain. 'She was jailed in a big prison on top of a mountain in Sichuan province. It rained all the time. So she hates the rain, and she hates climbing mountains, because she was kept on top of one,' says the friend. Luckily for Zhang, Beijing is dry and flat.

Criticisms have been raised that Zhang, who was 16 at the time of her family's downfall, could not have remembered conversations, clothes, and meals detailed in her book. Zhang has said that with her life in ruins, all she had were her reminiscences, so she developed a powerful memory. Her book is all about the power of memory when freedom of expression is denied.

'In China and the former Soviet Union, a person's most precious and rare activity is remembering - because memory is more reliable than a diary or a letter in supplying the real picture of society,' Zhang writes in the preface. 'Lots of people, when they are attacked or humiliated, destroy all their personal documents, and with them goes the record of the past. So, when the public comes to remember, what they have left are newspapers, commentaries and policy documents.'

Against such a reality, only the power of memory can stand testimony to the truth.

Like any great cultural achievement, the title of Zhang's book has already insinuated itself into everyday speech, despite - or maybe because of - its banishment. 'I saw a review the other day in a newspaper that ran: The Past is Immediately Forgotten,' says a friend of Zhang's, laughing. 'It's obvious that's a reference. I'm compiling a list of them.'