BEIJING (AFP) - The conviction of disgraced top politician Bo Xilai was less about eradicating ubiquitous corruption in China and more about warning Communist Party cadres to stay loyal to the new leadership or suffer the consequences, observers say.

President Xi Jinping, who took office earlier this year, has vowed to tackle both low-level "flies" and high-ranking "tigers" in an anti-corruption drive that has led to expectations that past and present political big-hitters could be targeted.

But despite the downfall of the former Chongqing party chief - jailed for life on corruption charges Sunday - the tough rhetoric is unlikely to be matched with action against endemic graft as long as the newly installed leadership can count on loyalty, experts say.

Bo's spectacular fall from grace came after he became a standard bearer for those who favoured his populist left-leaning policies.

Observers say this became more of a threat to the legitimacy of the reform-minded political elite than the sensational scandal that engulfed him, including the murder of a British businessman for which Bo's wife was convicted.

The former elite politburo member was convicted of taking 20.4 million yuan (S$4.15 million) worth of bribes.

It is an amount that pales into insignificance compared with the huge fortunes alleged to have been amassed by the families of Mr Xi and former premier Wen Jiabao in investigations by US media, said David Zweig from Hong Kong University of Science and Technology.

But he said that the objective of Bo's trial was not to uncover corruption, but to ensure he was silenced.

"They have really kept this small, which is an important message they are trying to send," he said, adding that Communist Party top brass do not want to discuss huge sums, "just a few million".

"They do not want to reflect on other people in the way that Bloomberg and the New York Times have both accused the Xi and Wen families of massive wealth."

Mr Zweig added that the ending of Bo's political career has the broader aim of weakening the party's left-wing elements.

"It is not just the standard purge," he said. "He will spend a lot of time in jail. It is a message to the left they do not have someone they can rally around here. He is done for."

Bo staged a feisty defence in court that surprised many observers, and his show of defiance was seen as a factor behind his heavy sentence.

He again erupted in anger when the life sentence was handed down, shouting out "Unfair!" and "Unjust!" according to the South China Morning Post. It did not say how it learned of the comments which were not in official accounts of the closed-door hearing.

Speculation has mounted in recent weeks that Beijing could take the drastic step of targeting an even higher-ranking figure and Bo ally, the recently retired Zhou Yongkang.

The former security tsar served until last November on the then nine-member super elite politburo standing committee, but Willy Lam, China politics expert at the Chinese University of Hong Kong, said a move to investigate him is highly unlikely.

"With Bo, Xi Jinping has made his point," said Mr Lam.

"Obedience to the party is more important to the party leadership than corruption." "All this going after big tigers is divisive and causes disunity among the factions, and this is why Xi will not go after Zhou Yongkang."

Bo's leftist revival during his tenure as party chief in the southwestern mega-city of Chongqing saw thousands of officials sent to the countryside to get closer to ordinary people, and the staging of mass concerts with "red songs" praising former leader Mao Zedong.

After his downfall, factions in the upper echelons of the Communist Party were reportedly split on how to handle him, and a year and a half passed following his detention before he went on trial.

"Many Chinese people liked Bo for his populist approach to politics and policy," said Mary Gallagher, director of the Center for Chinese Studies at the University of Michigan.

"His tendency to look for popular support hurt him with his colleagues, but I think it gave some citizens the taste for more democratic politics."

However, the lurid and widely publicised allegations that kept Chinese netizens spellbound only implicated his inner circle and close family, underscoring Beijing's tight control of the legal process.

"We have seen some kind of agreement - to not touch on intra-party struggles, to not implicate senior leaders - that certainly shows that the party is still in charge of the judiciary," said Joseph Cheng, a China politics expert at City University of Hong Kong.