He said the leadership should have followed the precedent of the former party boss Zhao Ziyang, who was held without trial under house arrest until his death, because investigating authorities cannot use torture to extract confessions from unrepentant senior leaders. Difficulties in staging what promises to be China's ''trial of the century'' have been compounded by a Reuters report on Thursday night that Mr Bo has grown a chest-length beard and gone on a hunger strike, requiring him to be taken to hospital. Sources with connections to the Bo family questioned the veracity of the report but confirmed he had been unwell and broadly unco-operative. ''We know China's court procedures are like a show,'' said the lawyer He Weifang, who played a leading role in rallying China's civil society against Mr Bo's disregard of legal processes when he was the party boss in Chongqing. ''So it requires good rehearsals beforehand and the need for Bo to be co-operative about his sentence,'' he said. ''They won't dare open the trial while there is any disobedience.''

Mr Bo divided the nation and its political elite with his neo-Maoist populism, ruthless disregard for legal institutions, and prodigious networking and self-belief. His leadership capabilities made him a potential threat to the new leader, Xi Jinping, say associates of Mr Xi. Mr Bo was sacked from his post in Chongqing on March 15 last year after his police chief sought refuge in a US consulate and told diplomats that Mr Bo's wife, Gu Kailai, had murdered an Englishman, Neil Heywood, by pouring cyanide down his throat. Gu and the former police chief were convicted last year and Mr Bo's fate appeared to be settled in September when the Politburo accused him of involvement in Heywood's murder; responsibility for his police chief's attempted defection; accepting huge bribes; and ''maintaining illicit relationships with numerous women''. Mr Bo is yet to be formally charged and details of the drawn-out investigation are opaque and contested.

A close friend of the Xi family, a liberal opponent of Mr Bo, said the case would proceed as planned after next month's National People's Congress because authorities had seized 22.7 million yuan ($3.5 million) from Mr Bo's Beijing home and presented him with a confession by his close business associate Xu Ming, who has also been detained. ''Bo may play tricks or lose his temper but when a stash of cash confiscated from his residence is presented to him, together with Xu Ming's confession, he had to confess,'' said the friend, who claimed close knowledge of the case. But a Bo supporter, Wang Zheng, a Beijing teacher with apparent ties to the family, said plainclothes investigators had waited until October 22 to take siblings to inspect the cash, stuffed inside seven locked suitcases inside the Bo family home in Beijing. ''Rumours of a hunger strike, which have been spreading for a long time, are not true,'' she said. A quarter of a century has passed since the party last convicted any of its top-ranking princelings for legal transgressions, in part because of the uncomfortable precedent that would be set for other powerful families.

The momentum towards Mr Bo's trial, conviction and political purge was seriously interrupted by a New York Times report in October that said the family of his great public opponent, Premier Wen Jiabao, had accumulated a $US2.7 billion fortune and hidden it beneath layers of holding companies and false identities. Bo family supporters have shown support during the Spring Festival break by visiting Gu's mother in her Beijing courtyard home, several associates said. But they have also taken care to avoid inflaming the political challenge for Mr Xi. Representatives from three of China's most powerful families have pulled out of a small princeling reunion scheduled for Saturday night, in order to avoid inflaming a delicate situation. The head of the China Development Bank, Chen Yuan, Mr Bo's politically active younger brother Bo Xicheng and his classmate Liu Yuan, the son of the former president Liu Shaoqi, would not attend, sources said.