The wife of disgraced Chinese politician Bo Xilai is all but certain to be found guilty of murder when she goes on trial Thursday, but will likely escape execution, legal experts say.

China's official news agency Xinhua has already declared that the evidence against Gu Kailai, who along with a family aide is accused of poisoning a British man with whom she and her husband did business, is "irrefutable".

That, said experts, left little doubt that Gu -- herself a former lawyer -- would be found guilty, and may indicate she has confessed to murdering Neil Heywood, who was found dead last November in his hotel room.

The scandal ended Bo's high-flying political career and exposed deep rifts in the Communist party ahead of a once-in-a-decade leadership handover, and Thursday's trial in the eastern city of Hefei will be China's most watched in years.

But it is expected to be brief at just one or two days, and closed to journalists, although British diplomats will attend -- an extremely rare concession in China.

Margaret Lewis, an expert on Chinese law at Seton Hall University in the United States, said it was unclear whether Gu's government-appointed lawyers would even mount a defence at all.

"It would be absolutely shocking if this case went to trial and there was not a guilty verdict," she told AFP by telephone.

"The conviction rate is exceedingly high across the board, even when you don't have tremendous political considerations on the table."

Communist party authorities ousted Bo as party chief for the southwestern megacity of Chongqing and from the powerful 25-member Politburo in the spring, putting him under investigation for violating party discipline -- usually code for corruption.

The scandal erupted in February when Bo's former right-hand man and police chief Wang Lijun fled to a US consulate to seek asylum after reportedly confronting Bo with information related to Heywood's murder.

Chinese activists fear the Communist leadership, keen to see the back of the scandal, is seeking use the high-profile murder trial to detract attention from the potentially politically explosive corruption allegations against Bo.

Gu was born into an influential family -- her father was the renowned general Gu Jingsheng -- while her husband Bo is the son of a Communist revolutionary, and China's state media has portrayed the case as a sign no one is above the law.

The Xinhua announcement said Gu feared Heywood posed a threat to her son's safety -- an indication, some experts believe, that she will be spared the maximum sentence.

"That could be considered -- and it occasionally is considered -- a mitigating circumstance, to have a so-called good motive for doing a bad thing," said Jerome Cohen, an expert on the Chinese legal system.

"Another factor that will affect the sentence is how she behaves," said Cohen, a law professor at New York University. "Is she being cooperative? Has she spilled the beans about everything they've been asking her about for many weeks?"

Xinhua's announcement on the charge against Gu was announced shortly after French architect Patrick Devillers flew to China to assist with the investigation after being detained at Beijing's request in Cambodia.

Devillers, 52, is understood to have been a close business associate and friend of Gu and Bo, but his role in the case is unclear and it is not known whether he will give evidence in court.

Intentional homicide, the charge Gu and her co-accused Zhang Xiaojun face, carries the death penalty, but courts can sentence those found guilty to as little as as three years in jail.

Gu is most likely to face a commuted death sentence, and to serve as little as 15 years in jail, said Cohen, adding that elite figures who are imprisoned normally find themselves in better-than-average conditions.

Experts said Zhang, who Xinhua has described as an orderly in Bo's home, would likely receive a similar sentence if he carried out the poisoning on Gu's orders.

"Relatively speaking the one who gave the order should face a heavier sentence, but the details are not clear," said Cheng Guangzhong, a professor at the China University of Political Science and Law.

"If he carried it out directly, putting the poison, etcetera, then he cannot avoid punishment. I reckon their sentences will be about the same."

Chinese rights lawyer Mo Shaoping said the trial was likely being held in Hefei because the city lies outside Gu and Bo's sphere of influence.

"They often change the location of trials if they feel that the influence of people in the main location is too big," Mo said. "They don't want these people to use their relationships to influence the case."