LONDON — A former UK border official and a retired Hong Kong police officer were given prison sentences on Thursday for spying on dissidents and critics of Beijing in Britain.

Border Force officer Peter Wai and Bill Yuen, a former superintendent in the Hong Kong Police, posed as police or intelligence officers to conduct surveillance and gather information about Hong Kong dissidents and pro-democracy supporters, prosecutors said.

Their targets included former Hong Kong lawmaker Nathan Law and activists they referred to as “cockroaches,” as well as British politicians critical of China, according to the prosecutors.

A jury found the two Chinese-British nationals guilty last month of breaching the National Security Act by assisting a foreign intelligence service.

Wai was also convicted of misconduct in a public office for using a government computer to seek information on people of interest to the Hong Kong authorities.

At London’s Central Criminal Court, Judge Bobbie Cheema-Grubb sentenced Wai, 41, to ten years, and Yuen, 66, to an eight-year term in prison.

She said the defendants’ “deliberate, concerted, and serious” actions had left those targeted in fear and distress.

Wai was an officer in London’s Metropolitan Police before joining the UK Border Force. Yuen was the office manager at the Hong Kong Economic and Trade Office in London, the official overseas representative of Hong Kong’s government.

Helen Flanagan, commander for Counter Terrorism Policing London, said that “the activity of Wai and Yuen was truly chilling.”

“They were spying and targeting individuals in the UK who were pro-democracy campaigners and were simply protesting against the Hong Kong and Chinese government and authorities and seeking sanctuary in the UK,” she said.

Chinese Ambassador Zheng Zeguang was summoned to the British Foreign Office after the convictions last month.

At the time of the convictions, China’s Embassy in the UK called the case a political farce intended to support anti-China forces who had fled to Britain.

The Hong Kong government said the allegations “are absolutely unrelated” to the government or the Economic and Trade Office.

British authorities “initiated the case on groundless accusations, abused law and manipulated judicial procedures to secure conviction,” it said in a statement.