China's most politically sensitive trial in three decades opened on Thursday with police dragging two protesters away from a courthouse where the wife of ousted Politburo member Bo Xilai is expected to be swiftly convicted of murder.

The two Bo supporters were dragged kicking and yelling into a police car after they had appeared outside the courthouse in the eastern city of Hefei, singing patriotic songs that were the trademark of Bo's populist leadership style and condemning the trial as a sham.

"I don't believe it. This case was decided well in advance," Hu Jiye, a middle-aged man wearing a T-shirt and baseball cap, told foreign reporters at the rear of the court building.

Hu and his friend were then shoved by plainclothed police into a car. His companion, also a middle-aged man, struggled, yelling "Why are you taking me? Why are you taking me?"

The trial of Bo's wife Gu Kailai is seen by many Chinese as part of a push against Bo, an ambitious populist who made powerful enemies as he campaigned to join the next generation of top central leaders.

Bo was formerly considered a contender for the inner sanctum of power - the party's Politburo Standing Committee - in a once-in-a-decade leadership transition that is currently underway. The new leadership is expected to be unveiled in October.

Gu and her co-accused, a family aide, are charged with poisoning Briton Neil Heywood last year in a case that has rocked the Communist Party leadership.

A Hefei official told reporters the hearing was likely to end at around 11 am local time (3 am GMT), when a court official would give a statement to reporters. It was not clear if the official was indicating the end of the trial, or simply Thursday's session.

There was no word when the verdict or sentencing would be announced with estimates ranging from a day or two to several weeks, although most experts expect a quick conviction.

Dozens of policemen threw a security cordon around the court building in Hefei, the capital of Anhui province, with some surrounding streets blocked off with cones.

Entry to the courtroom was restricted but two British diplomats were invited to be present because of the nationality of the victim.

Journalists were not being allowed in, and it appeared any coverage would be only from state media outlets.

HEAVY RAIN

The British envoys, arriving in heavy rain at the granite-and-glass courthouse, told a scrum of reporters outside the building they would not discuss the case.

Gu, herself a career lawyer, is set to be defended by a state-appointed lawyer with meagre experience in criminal cases, leaving little doubt she will be convicted.

The state has decided who will represent Gu, denying her the use of a family lawyer - a move that has also prompted Gu's 90-year-old mother, Fan Xiucheng, to recently complain to the Justice Ministry, according to a source close to the family.

"The answer (from the ministry) was that the legal process did not have to be fully carried out in this case and that Fan should stop pestering them," the source said.

The trial of Gu, glamorous daughter of the ruling Communist Party aristocracy, is the most sensational since the conviction of the Gang of Four more than 30 years ago for crimes during the 1966-76 Cultural Revolution.

But despite British calls for the case to be handled fairly and to unearth the truth around Heywood's death, her defence has instead been entrusted to two provincial lawyers.

The two lawyers, Jiang Min and Zhou Yuhao, could not be reached for comment but a search of public information shows the more senior attorney, Jiang, is a specialist in financial cases and that neither has any obvious connection to the Bo family.

A newspaper profile of Jiang from 2005, which was posted on Jiang's own website, quoted him as saying that he was 'an expert in financial law, who rarely conducts criminal defences', although he has represented some officials accused of corruption in the more than 20 years he has been practising law.

Little is known of Gu's other lawyer, Zhou, except that he, like Jiang, is from Anhui province. Provincial capital Hefei is a bustling city more than 1,000 km (650 miles) east of the scene of the alleged crime - Chongqing, the vast municipality formerly ruled by Bo.

Gu and family aide Zhang Xiaojun face the death penalty if convicted of poisoning Heywood, a former family friend, last November in a dispute that has not been spelt out in the very little official information released on the case.

But many legal experts expect Gu will be convicted but only sentenced to a lengthy jail term.

GREEDY WIFE OR PROTECTIVE MOTHER?

Police sources initially claimed Gu had poisoned Heywood in a dispute over an illicit financial transaction she had wanted him to help her complete, and they portrayed Gu as a greedy wife who was translating her husband's connections into dollars.

But when Gu was formally indicted, the official allegation instead hinted at a personal motive, saying Heywood had made unspecified threats against her son Bo Guagua, a factor that may count as a mitigating circumstance and help Gu avoid execution.

The younger Bo, who is believed to be still in the United States after graduating from Harvard this summer, told CNN in an e-mail that he had submitted a witness statement to the court.

"I hope that my mother will have the opportunity to review them," he added. "I have faith that facts will speak for themselves." CNN said he did not elaborate.

The trial and sentencing of both Gu and Zhang are widely seen as a prelude to a possible criminal prosecution of Bo, who is being detained for violating party discipline - an accusation that covers corruption, abuse of power and other misdeeds.

Bo, who was a favourite of party leftists by promoting himself as a friend of the poor and an enemy of corruption, was sacked as Chongqing party chief in March after his police chief, Wang Lijun, identified Gu as a suspect in Heywood's death.

On Thursday morning, there was no sign of Gu's elderly mother, nor of any members of Heywood's family in or around the courtroom.