China’s Ministry of Foreign Affairs has strongly condemned the UK for “abusing the law and judicial process” after a British court found two men linked to the Hong Kong Economic and Trade Office in London guilty of spying on activists.

Bill Yuen Chung-biu, the London office’s manager, and Peter Wai Chi-leung, who ran a security firm, were found guilty on Thursday of assisting a foreign intelligence service, two years after their arrests thrust Hong Kong’s overseas promotion offices into the global spotlight.

Ministry spokesman Lin Jian described the charges on Friday as lacking “factual basis” and accused the United Kingdom of “securing the conviction by abusing the law and judicial process”.

“Such groundless accusations and smears against China are nothing but a typical political stunt. China strongly deplores and firmly opposes it, and has lodged serious protests against the UK,” he said.

Following the verdict, the Hong Kong government also said the allegations were “absolutely” unrelated to the administration, while maintaining that the office was conducting its duties in accordance with legislation in the United Kingdom.

“Nor are we party to the case,” he said. “We firmly oppose any unfounded allegations against the [Hong Kong] government and the London [office].”