The activist, Tony Chung, was imprisoned after advocating for the territory’s independence. Even after his release, he said, his situation remained oppressive.
A political activist in Hong Kong previously imprisoned under its sweeping national security law said he had fled to Britain and would apply for asylum there, becoming the second high-profile dissident this month to announce going into exile from the territory.
The activist, Tony Chung, revealed on Thursday that he had arrived in Britain, and, in several social media posts, said that he had decided to leave Hong Kong after enduring oppressive restrictions, pressure to act as informant and severe stress after his release from prison in June.
Mr. Chung, 22, was sentenced to three years and seven months in prison in 2021 after becoming an outspoken proponent of independence for Hong Kong — an idea that is anathema to Communist Party leaders in China, which rules the territory. He was released early, but police officers continued to monitor him closely, he wrote in his account on Instagram. He won their approval to take a brief vacation in Okinawa, Japan, and while there bought a ticket to Britain, he wrote.
“This also means that for the foreseeable future, it will be impossible for me to return to my home, Hong Kong,” Mr. Chung wrote. “Although I had previously anticipated that this day would come, my heart still sank at the moment I made up my mind. Ever since I joined social movements from the age of 14, I have always believed that Hong Kong is the only home for the nation of Hong Kong, and we should never be the ones who must leave it.”
Mr. Chung’s departure from Hong Kong was earlier reported by The Washington Post. The Hong Kong police did not respond to emailed questions about him on Friday.
Mr. Chung joins a growing number of Hong Kong activists and pro-democracy organizers who have left since the territory imposed a national security law in June 2020 in response to huge pro-democracy protests there for much of 2019, which sometimes flared into violent clashes between demonstrators and police officers. The law established the judicial and police machinery to drastically constrict political freedoms in Hong Kong, a British colony until 1997 that after its handover to China retained its own system of laws and limited democratic competition for a share of seats in the city’s legislature.
In early December, Agnes Chow, a former pro-democracy student activist in Hong Kong who had served time on some charges connected to her political activities and was still under investigation for others, announced that she had gone to Canada and was defying instructions to report to the Hong Kong police, a condition of her bail. She said that after her release, the police had taken her on an indoctrination tour in mainland China, seeking to convince her that Communist Party rule was all for the better.
“Perhaps I will never go back again in my lifetime,” she wrote of Hong Kong.
Mr. Chung described similar efforts by the Hong Kong officers who monitored him.
Mr. Chung became the third person sentenced under the security law after prosecutors accused him of secession by promoting independence for Hong Kong, on social media and through a now-disbanded group, Studentlocalism. He was also sentenced on a money laundering charge related to donations that he received in support of the group.
After his release from prison, he tried to regain his economic footing with a temporary job, but police officers ordered him not to take it, without explaining why. Officers offered to pay Mr. Chung to act as an informant, and at meetings pressed him for details about places he had gone and people he had met, including his elementary school classmates, he wrote.
The expansion of such informal oversight over ex-prisoners showed how Hong Kong’s security police have at least partly replicated the methods of the mainland Chinese authorities, said Thomas Kellogg, the executive director of the Georgetown Center for Asian Law, who has studied how Hong Kong’s national security legislation has been enforced.
“What we’re seeing with Agnes, Tony and others is the importation into Hong Kong of some of these elements of the police state,” Mr. Kellogg said in a telephone interview.
The Hong Kong Democracy Council has estimated that over 1,700 people in the territory have been imprisoned for protest activities, organized political opposition and related charges, including property damage, under the national security crackdown. How many have been released, and how many have left the territory, is less clear, experts say.
“You’re seeing a little boomlet of people who have decided to leave,” Mr. Kellogg said. “There’s a lot of different permutations, but the end result is the same in quite a lot of these cases: People are running for the exits, if they can.”
Abroad, Hong Kong activists may still face intimidation. In July, the territory’s government announced bounties of 1 million Hong Kong dollars, or around $128,000, for information leading to the apprehension and prosecution of eight activists who had fled abroad.
Such tactics mean that some activists who leave Hong Kong may choose to live under the radar, rather than exposing their families back home to police questioning and pressure, said Patrick Poon, a visiting researcher at the University of Tokyo who monitors human rights in Hong Kong.
“But some others think, ‘Well, I don’t have any contact with my family in Hong Kong any longer,’” Mr. Poon said. “Especially some of the younger ones defy such threats.”
Mr. Chung said that he planned to study in Britain, and suggested that he might remain politically active. “I believe that as long as the Hong Kong people never give up, the seeds of freedom and democracy will sprout alive again,” he wrote.