Both Conservative and Labour members of parliament have called for allegations of police brutality in Hong Kong to be investigated – a claim rejected by the force – piling pressure on the British officers who continued to serve after the 1997 handover.

Some of these officers played a role in quelling the protests, triggered by a bill that would have allowed suspects to be sent to mainland China for trial. The bill was later withdrawn.

The Hong Kong police have not responded to a request for comment.

“These police officers are the shame of Britain. For too long they have been allowed to live some kind of postcolonial dream in Hong Kong, beating up people with impunity and overseeing truly shocking atrocities,” said Luke de Pulford of London-based group Hong Kong Watch, who co-launched the campaign with Law.

He added that “at least five” Britons had been identified. He refused to name them, but said initial legal advice suggested that they would likely have a case to answer on torture.

The Crown Prosecution Service said that “in some cases” private prosecutions in the English courts must seek the consent of the attorney general or director of public prosecutions.

“When it comes to it, I hope the UK attorney general and the director of public prosecutions will see that this case is clearly in the public interest,” Law said. “British citizens have been responsible for heinous brutality in Hong Kong, and the UK must hold them to account.”

Michael Polak, a lawyer in Britain, said the action was necessary as the integrity of Hong Kong’s Independent Police Complaints Council had been called into question.

Hong Kong protests: policeman facing private prosecution over shooting launches High Court bid to have case thrown out

Anyone who had been subject to “severe pain and suffering, physical or mental” from the police officers, including the illegitimate use of tear gas, could submit evidence to the campaign, Polak said.

Torture is considered a matter of universal jurisdiction under English law, meaning that the British courts could decide on acts committed in, for example, Hong Kong.

Offences covered by universal jurisdiction include certain war crimes, torture and hostage-taking and anyone can apply to the courts for an arrest warrant to ensure those guilty of these crimes abroad face justice in Britain.

Previous cases involving such judicial exercise of universal jurisdiction have usually involved war crimes.

In Hong Kong, Democratic Party lawmaker Ted Hui Chi-fung raised HK$3.38 million (US$434,000) through crowdfunding and launched a private prosecution against a police officer who shot a protester with a live round last year.

The case has been given the green light to proceed by Eastern Court, with the officer scheduled to enter his plea on a count of shooting with intent and two firearm charges on August 31.

But on Monday the officer’s lawyer filed an application at the High Court for a judicial review, seeking to quash his prosecution.

They argued that it was a violation of Article 63 of the Basic Law, the city’s mini-constitution, which said the Department of Justice “shall control criminal prosecutions”.

Hui is also considering another prosecution against the officer who repeatedly drove a motorcycle into a crowd during a separate protest on November 11, the same day as the shooting.

He he has offered a HK$200,000 reward for the rider’s identity.