Fallen Chinese politician Bo Xilai's spirited self-defence in court was likely condoned by the authorities to give a varnish of fairness to a trial in which the verdict is already decided, analysts say.

Bo, who was tipped for top office ahead of a once-in-a-decade leadership transition last year, hurled insults at his accusers and calmly tried to bore holes in the prosecutors' logic.

His display on the first day of his trial Thursday at the court in Jinan was in contrast to the meekness usually shown by defendants in high-profile Chinese cases.

But analysts said that while Bo's being allowed to speak out gave the process a sheen of transparency, it will have no effect on the result.

Steve Tsang, an expert on Chinese politics at Britain's University of Nottingham, said the trial had been agreed on by the top leadership with the verdict and sentence already determined.

"Therefore, almost whatever he does the court is going to act in accordance with the script prepared beforehand," he said.

Bo was allowed to speak out via the release of near-real-time court transcripts sent via social media -- although it was not clear how complete the accounts were.

"I think the authorities will say that they have tried to give him an opportunity to defend himself," said Willy Lam, an expert on Chinese politics at the Chinese University of Hong Kong.

"So it gives some credence to the spin which Beijing is trying to give this, that they are now more willing to observe the rule of law and so forth."

On Friday the state-run China Daily's front-page headline read: "Bo Xilai denies charges of bribery." A second story was titled: "Case breaks ground for transparency."

The hearings also give Bo, a scion of Communist Party royalty as the son of a legendary party figure, a chance to save some face with his supporters.

"You can say that Bo has maintained his reputation as a maverick, as a charismatic leader who challenges party authority sometimes," Lam said.

"So I think you can say that he has won something, at least, particularly compared to his wife and other victims of power struggles."

Bo's spouse, Gu Kailai, was convicted last year of the murder of British businessman Neil Heywood, whose death sparked the drama that led to her husband's downfall.

"He does strike a pose of defiance. But I don't think either way it will affect the outcome," Lam said.

He Weifang, a law professor at the prestigious Peking University, said the court must have received permission from higher authorities to publish so much of the dialogue.

"I think that officials think that by doing it this way they can be more persuasive, and can tell people more clearly that the process is just," he said.

"Of course it's not a completely fair process," he added, while expressing surprise at what he called "the comparative level of openness".

Nottingham's Tsang said Bo was clearly aware of what was going on.

"He knows the system, he knows how it works and therefore he will know that he is probably going to have a jail sentence not less than what his wife got, so at least 15 years," Tsang said.

"He will not be executed and he will not regain his freedom while the current political set-up remains as it is."

Authorities were taking a "calculated risk" by allowing Bo to speak out and potentially drum up support for his cause, Tsang said, but he emphasised they have most probably reached a deal with him already and that he has "in principle" agreed.

Observers have speculated that Bo wants to protect his son, Bo Guagua.

The son is studying law in New York -- and was himself implicated in alleged bribery during Friday's proceedings.

Bo knows that he can rely on a long-standing practice in the Communist Party that, since the Cultural Revolution, the next generation is left exempt from internal factional and power struggles, Tsang said.

"If the top leadership now goes back to punish Bo Guagua for his father's defiance in court, then they are actually changing the game somewhat," he said.

"And then they will have to start to worry about if they themselves fall from power will their relatives, will their next generations, also suffer?

"That is a pretty strong deterrent to the top leadership from punishing Mr Bo by doing something about his son and that may well in fact be the calculation behind Mr Bo's defiance.

"He's got nothing to lose."

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