Bill Yuen, 65, a dual Chinese-British national, is on trial at the Old Bailey under the National Security Act alongside Border Force official Peter Wai, 38.

Wai and Yuen are jointly charged with assisting a foreign intelligence service between December 2023 and May 2024, and with a second charge of foreign interference on May 1, 2024.

Wai is also accused of misconduct in a public office by misusing his access to a Home Office computer system.

Prosecutors say the men gathered intelligence and carried out surveillance on Hong Kong pro-democracy activists and dissidents living in the UK. Both deny all charges.

During cross-examination, prosecutor Duncan Atkinson suggested Yuen had never really left the employ of the Hong Kong government.

He said Yuen had instead moved seamlessly from a 20-year career in the Hong Kong police to a job at the Hong Kong Economic Trade Office (HKETO) in London only months after retiring.

- 'Not dumb' -

Yuen retorted that "if I really did something illegal for my authorities you would not pick up such suspicious things" referring to evidence, such as WhatsApp messages between him and Wai, cited during the trial.

"I'm not dumb as that."

"If they really wanted to do so they would hire a Hong Kong intelligence officer to do it," he added, during one of several heated exchanges.

"They wouldn't ask a 66-year-old man to do this and end up in this embarrassing situation."

Yuen insisted his return to work had come at his wife's prompting and after seeing a job advert for the role and not at the behest of the Hong Kong authorities.

The prosecutor pressed him on messages he sent asking Wai to "pay special attention" to British MPs and local councillors supportive of pro-democracy protesters and to "take some photos and do some research".

Yuen said the purpose was to avoid "embarrassment" to his employer, not to gather intelligence.

He also denied asking Wai to carry out surveillance on high-profile Hong Kong pro-democracy activist Nathan Law, despite Wai sending him photographs of Law's car and number plate.

The pair were arrested after a team of operatives allegedly forced their way into the flat of Monica Kwong, a Hong Kong fraud suspect, in Pontefract, West Yorkshire on May 1 2024.

Tens of thousands of people, including democracy activists wanted by Chinese authorities, have moved to the UK since Hong Kong enacted a draconian National Security Law in mid-2020.