An American lawyer working in Hong Kong lost his appeal Tuesday and was jailed for assaulting a plainclothes policeman when he intervened in a confrontation between the officer and members of the public three years ago.

The confrontation occurred toward the end of the huge and often violent democracy protests that rocked the financial hub.

At the time, the city's 30,000 police officers were allowed to carry retractable batons during off-duty hours to protect themselves during a period when the popularity of law enforcement had plummeted.

Samuel Phillip Bickett, 37, thought he was breaking up a fight inside a Hong Kong Subway station in December 2019 as the police officer did not declare his identity, defence lawyers had argued earlier.

The former compliance director at Bank of America was sentenced to four and a half months in prison last July, and spent 45 days behind bars before he was granted bail pending his appeal.

On Tuesday, High Court Judge Esther Toh dismissed his appeal, saying the event took place during "a most violent chapter in the history of Hong Kong" where off-duty police were beaten up.

"Police officers or any public officers who are carrying out their public responsibilities must be protected when in the execution of their duties," Toh said, returning Bickett to jail to serve out the remainder of his sentence.

The American maintained his innocence and said he would further appeal his case.

Samuel Phillip Bickett thought he was breaking up a fight at the time as the police officer did not declare his identity, his lawyers said
Samuel Phillip Bickett thought he was breaking up a fight at the time as the police officer did not declare his identity, his lawyers said AFP / Peter PARKS

"Today's ruling is just the latest indication that the judiciary's reputation for applying the law rationally, fairly and equally is in danger," he said in a statement.

"In a society with rule of law, police officers do not have free rein to do whatever they want."

The December 7, 2019, confrontation occurred after Senior Constable Yu Shu-sang in plainclothes forcibly stopped a young man who had allegedly jumped a turnstile.

Bickett said he believed the officer's use of force to be unlawful, noting that Yu and another man had been "beating and choking" the man with a baton before he intervened.

In the ensuing scuffle, which was caught on camera, Bickett grabbed the officer's baton, stepped on his chest and hit him in the face several times -- a move his lawyers deemed as "reasonable force" to halt Yu's actions.

But Toh rejected the argument, saying that Yu striking the American was "entirely natural and appropriate" as the police officer was "outnumbered in front of a hostile crowd".

Public trust in the Hong Kong Police Force was severely hammered during the 2019 democracy protests, where violent clashes resulted in over 10,200 arrests and hundreds of officers wounded.

More than 2,700 of the arrestees have been prosecuted for a wide range of offences including rioting and unlawful assembly, while no officer was brought to court for misconduct.