Chung Biu Yuen, 64, and Chi Leung Wai, 39, also known as Peter Wai, pleaded "not guilty" at the Old Bailey to two charges under Britain's National Security Act, a law passed last year to give new powers to target threats from foreign states.

The men, both dual Chinese and British citizens, are accused of assisting a foreign intelligence service between December 2023 and May this year by "agreeing to undertake information gathering, surveillance and acts of deception" in Britain.

They are also accused of conducting "foreign interference" by forcing entry into a residential address on May 1.

Police have said the alleged actions were carried out on behalf of the intelligence service of Hong Kong, a former British colony. The Chinese Embassy in London has accused Britain of fabricating the charges and said it had no right to interfere in Hong Kong's affairs.

Yuen is a retired Hong Kong police officer and an office manager at the city's Economic and Trade Office in London. Wai worked as a UK Border Force officer and as a volunteer part-time officer for the City of London Police.

Their trial, expected to last four weeks, has been provisionally set for March 10.

A third man who was accused of the same offences, Matthew Trickett, 37, a former British Royal Marine who worked as an immigration officer and private investigator, was found dead in a park in Maidenhead, west of London, in May, not long after the trio were charged.

Hong Kong was under British rule for 156 years before reverting to Chinese sovereignty in 1997. There have been growing tensions between the two nations over a national security crackdown since sometimes violent pro-democracy protests swept the territory in 2019.

British Prime Minister Keir Starmer called last month for "consistent, durable" relations when he met Chinese President Xi Jinping as part of efforts to thaw ties.