Bo Guagua, the high profile son of toppled politician Bo Xilai and his wife Gu Kailai, has defended his "upright" and dutiful father in his first comments on the toppled politician since scandal engulfed his family.

His comments come shortly after Chinese leaders announced that they had expelled the former Chongqing party secretary from the Communist party and that he would face criminal charges.

Bo Xilai was once tipped for possible promotion in this autumn's leadership transition. But his spectacular fall culminated in Friday's announcement that he was accused of offences including abusing power and taking massive bribes.

He was also accused of bearing "major responsibility" in relation to his wife's murder of a British businessman and maintaining improper sexual relationships with several women.

"Personally it is hard for me to believe the allegations that were announced against my father, because they contradict everything I have come to know about him throughout my life," his son wrote in a message posted online. He confirmed via email that he had written the statement.

"Although the policies my father enacted are open to debate, the father I know is upright in his beliefs and devoted to duty. He has always taught me to be my own person and to have concern for causes greater than ourselves. I have tried to follow his advice.

"At this point, I expect the legal process to follow its normal course, and I will await the result."

Bo Guagua graduated from a postgraduate course at Harvard's Kennedy School this summer - having previously studied at Oxford - and is thought to remain in the United States.

He has said little since his parents' detention in spring this year, although he confirmed he had given a witness statement to his mother Gu Kailai's trial. He said at the time he had faith that the facts would speak for themselves.

Gu was convicted of murdering British businessman Neil Heywood - who was friends with Bo Guagua - last month and handed a suspended death sentence.

Prosecutors alleged she killed the 41-year-old Briton because he had threatened her son over a business dispute. An unofficial account of the trial said the court heard Heywood had demanded millions of pounds from the family and at one point held Bo Guagua captive at a house in the UK - allegations that friends of the dead man strongly disputed.

Bo Guagua was a subject of fascination long before his father's fall, thanks to his flamboyant lifestyle at Oxford. Pictures of him partying and pretending to urinate against a college gate with friends were not shocking by Western standards, but raised eyebrows in China, where the "princeling" children of powerful leaders are supposed to be more discreet.

In a separate statement issued earlier this year he attempted to lay "rumours and allegations" to rest, writing that his "extracurricular-activities enabled me to broaden my perspective, serve the student community, and experience all that Oxford has to offer".

He added that his tuition and living expenses at Harrow, Oxford and Harvard were funded exclusively by academic scholarships and his mother's savings. The details of those scholarships remain unknown.

"Guagua is smart and an accomplished debater," said a family friend who met the couple and their son in the US and China.

"He has excellent presentation skills and a logical mind. I wouldn't exactly call him a playboy. But he's certainly trendy. He likes the good things."

The friend said he was respectful to elders but added: "Behind the politeness there is a cockiness. He's very much aware he comes from the elite."