Three decades after his death the face of Mao Tse-tung still stares out over the huge expanse of Tiananmen Square in central Beijing. Though the authorities now admit that the founder of Communist China was “70% right, 30% wrong”, the man who led the greatest revolution since the second world war remains a sacrosanct figure in the world’s most heavily populated nation.

This summer, though, his reputation has been comprehensively demolished in the West by the bestselling biography, Mao: The Unknown Story, by Jung Chang, author of the perennial bestseller Wild Swans, and her historian husband, Jon Halliday. It blames Mao for 70m deaths — far more than Hitler or Stalin.

Though travellers have brought in copies in their luggage, and it has been reviewed in newspapers in Hong Kong, the book is not on sale in mainland China. English-language newspapers in the Far East that carried articles about it were banned. On internet chat sites the censors have moved in to delete any postings critical to the man hailed as the Great Helmsman of China.

Chang’s book, published by Jonathan Cape, has attracted most attention for its portrayal of Mao as an utterly ruthless, evil figure who eliminated enemies by purges, poison and murderous traps, abandoned three wives and was driven by ambition, not ideology. But the shock might not be so great in China as in the West, given the killings and disasters the country suffered in the 20th century, the general absence of humanity among its leaders, and the personal experience so many people had of the disasters of the past half-century.

In its 70-30 valuation of Mao, Beijing is willing to admit to one major fault — the Cultural Revolution he launched in 1966 to assert his authority by unleashing the Red Guards on the political establishment, which he feared was escaping his control. But this disavowal is used for a political purpose, to argue how important it is to maintain stability and how dangerous political reform would be.

Otherwise, Mao remains untouchable in China, though it has become increasingly clear he is a figure surrounded by self-created myths that no longer hold water. There is a very good reason for this, which explains why the new biography and other recent research represent a real and present danger for the rulers of the last leading state run by a Communist party. Remove the props of Maoist history and you bring into question the foundations of the party’s legitimacy to govern 1.3 billion people and head an emerging global economic superpower.

Four elements lie at the heart of the Mao story. All are totally or largely false.

A key assertion is that he was a pure nationalist who put his country first and led the only true resistance to the Japanese invasion of China from 1931 to 1945. This is particularly important today, when the wilting appeal of communism has led the authorities to promote nationalism to win public support, particularly against Japan. Mao as patriotic hero is a potent recruiting sergeant.

But this new biography shows how a foreign leader, Joseph Stalin, aided and directed Mao’s rise. Halliday is a Russian expert, and has extracted a wealth of documentation from the Moscow archives. The Soviet role in establishing the Chinese Communist party around 1920 was already known, but what is new is how, despite some divergences, Mao followed Stalin’s dictates to win power.

Only the Kremlin could provide the political backing, money and arms he needed. Since Stalin played a double game in China, maintaining relations with the Nationalists and supplying Mao’s great opponent, Chiang Kai-shek, with arms, Mao’s greatest fear must have been that Moscow would desert him in the name of realpolitik. To avoid that, he kowtowed to Moscow — even after he achieved power he rose to his feet during a visit by a Soviet envoy to cry out three times “ May Stalin live ten thousand years”.

Another big hole in the Mao-as-patriot story comes during the full-scale war that broke out with Japan in 1937. Apart from one offensive, of which the Chairman disapproved, the Red Army avoided conflict, saving its resources for civil war with the Nationalists after Tokyo’s defeat. Petr Parfenovich Vladimirov, the main Soviet adviser at Mao’s headquarters, makes this evident in his diary, which was published in 1974 in India but escaped attention until recently.

Communist forces, Vladimirov noted in 1942-43, “have long been abstaining from both active and passive action against the aggressors”. Instead, they were ordered to retreat and seek truces. Visiting battle areas a little later, a US unit found that Communist units had struck non-aggression agreements with the invaders. Trade flourished across the lines.

Nor was this all. The Communists maintained contacts with the collaborationist regime set up by Japan. Mao even floated the idea of a ceasefire with Japan in northern China.