A UK immigration officer has been found guilty of working for Chinese intelligence as part of a "shadow policing operation".
Chi Leung "Peter" Wai, 40, used his access to the Home Office computer system to track Hong Kong dissidents based in the UK through the main immigration database.
He was found guilty under the National Security Act of assisting a foreign intelligence service alongside Chung Biu "Bill" Yuen, 65, who was initially his contact with the Hong Kong authorities. Wai was also found guilty of misconduct in public office.
Chinese ambassador Zheng Zeguang will be summoned by the Foreign Office after the two men were found guilty.
Security Minister Dan Jarvis said the men's activities were "an infringement of our sovereignty and will never be tolerated".
"We will continue to hold China to account and challenge them directly for actions which put the safety of people in our country at risk," he added.
The jury could not agree on a charge against both men of foreign interference by forcing entry into the home of an alleged fraud suspect originally from Hong Kong in West Yorkshire.
The prosecution said it would not be seeking a retrial. The defendants were remanded into custody to be sentenced on a date to be fixed on 15 May.
Wai started working as a Border Force officer at Heathrow Airport in December 2020, which gave him access to a vast database of information about foreign nationals in the UK.
He searched it on his days off and sick days, earning money on the side by tracking Hong Kongers who had fled pro-democracy crackdowns for his Chinese contacts. There seems to have been no checks on his access to the database to prevent him doing this.
But he had been providing information on dissidents before then, referring to them in messages as "cockroaches".
Yuen became his contact with Chinese authorities. A former Hong Kong police officer, he worked as the office manager of the Hong Kong Economic and Trade Office (HKETO) in London.
The pair were introduced in 2017 and by the middle of 2021, Yuen had become Wai's handler - to whom he reported to directly about the activities of Hong Kong dissidents and pro-democracy protesters in the UK.
The court also heard "special attention" was paid to British politicians, such as Conservative MP Sir Iain Duncan Smith.
Head of Counter Terrorism Policing London Cdr Helen Flanagan said the pair's activity had been "both sinister and chilling".
Wai also drew a fellow Border Force officer, an ex-Royal Marine called Matthew Trickett, into his surveillance of Hong Kong dissidents, the court heard.
Trickett was found dead in a suspected suicide soon after they were caught by counter-terrorism police.
Wai, who holds both British and Hong Kong passports, had many jobs - including as a Metropolitan Police officer from 2015 to 2019.
He was in the Royal Navy for eight years, and worked for a company providing security for events in Chinatown. Wai had also set up his own company, D5 Security.
After leaving the Met, he became a volunteer constable for City of London Police.
Yuen had moved to London within days of retiring from the Hong Kong Police Force in 2015 to join his wife and two children, taking advantage of his dual British-Hong Kong citizenship.
Soon afterwards, he started working at HKETO. The office was set up to promote trade between Hong Kong and the UK, but became increasingly politicised after the 2019 protests in Hong Kong.
He and Wai were introduced at a restaurant in London's Chinatown by Chu Ting Tang, a prominent figure in the area is known to be sympathetic to the Chinese government's policies in Hong Kong.
When Wai started working at Heathrow, he sent a message to the former chief superintendent of Hong Kong Police's Criminal Intelligence Bureau Eddie Ma, who still had links to the Chinese state.
"Will not let any cockroaches in," Wai wrote.
When he later sent Ma some information about recently-arrived Hong Kong dissidents, Ma wrote back: "The head office seems to be interested at these informations."
Wai later began working with his fellow Border Force officer Trickett - who was also doing private security work to supplement his Home Office income - to gather information on Hong Kong dissidents.
In 2023, Hong Kong's chief executive John Lee Ka-chiu, its most senior politician, put bounties of HK$1m (around £100,000) on the heads of some of the pro-democracy campaigners, saying they would be pursued "for life".
The Chinese government also announced "Operation Fox Hunt" and "Operation Sky Net" to track down fugitives from the law.
In November 2023, Trickett was tasked by Wai to arrange for high-profile Hong Kong activist Nathan Law to be followed to the Oxford Union. He was one of the men with a HK$1m bounty on his head.
Another man who was targeted for surveillance by Wai's group was Finn Lau, he also had a HK$1m bounty for his arrest.
He was a high-profile democracy protester in 2019 and 2020, who escaped after being arrested in Hong Kong. He was also mysteriously beaten up in London five years ago.
"To be frank, I don't feel safe in the UK regarding the spying risk," Lau told the BBC.
"That's why we have been taking different sorts of measures to try to protect ourselves - like being cautious all the time, looking around, trying to even adopt some maybe anti-following tactics."
In April 2023, Wai - still a Border Force officer - provided security during the visit to London of Hong Kong's financial secretary Christopher Hui.
Using his City of London police identity card, Wai threatened to arrest a protester who was campaigning against Hui's visit, even though he had no official policing role that day.
By 2024, the security service MI5 had become aware of the activities of Wai and his group.
The men had started an operation to find a woman called Monica Kwong, who had been accused of stealing money from her employer in Hong Kong - something she strongly denies.
Using his access to the Atlas database, Wai tracked her down to her flat in Pontefract where she was living with her young son.
He confirmed her presence using the fake delivery of a parcel.
Wai started a surveillance operation on her flat and, on 30 April 2024, Tina Zou, the woman who claimed Kwong owed her money, flew to Heathrow with an entourage of colleagues and former Hong Kong police officers.
In an operation organised by Wai and Trickett - with Yuen's knowledge - Zou and some of her employees travelled up to Pontefract for what appears to have been an intended showdown with Kwong.
After Kwong failed to answer the door to her flat, the group became increasingly desperate to find her - using a "snake camera" to film under her door.
Trickett left a note claiming to be "Dave from maintenance", and then poured water under her door saying there was a leak.
Eventually, on 1 May 2024, the group broke into the flat, finding it empty. An audio bugging device left by MI5 recorded the whole thing.
When police moved in, Wai threw a fake warrant card that suggested he was a superintendent in the City of London Police out of the window.
The jury could not agree on whether events in Pontefract amounted to "foreign interference".
After Yuen, Wai and Trickett were charged and made their first appearance in court, Trickett was found dead in Grenfell Park, in Maidenhead, in a suspected suicide.
His inquest will be held in November.
Additional reporting by Maia Davies.
