Three men have been charged under the National Security Act with assisting the Hong Kong intelligence service and foreign interference.
All three appeared in custody at Westminster Magistrates' Court on Monday.
The Metropolitan Police said the investigation was not related to a separate case involving Russia.
A total of 11 people were detained under the National Security Act as part of the investigation.
The three men charged are: Chi Leung (Peter) Wai, 38, of Staines-upon-Thames, Surrey; Matthew Trickett, 37, of Maidenhead, Berkshire; and Chung Biu Yuen, 63, of Hackney, east London.
Between 20 December 2023 and 2 May, they are accused of agreeing to undertake information gathering, surveillance and acts of deception that were likely to materially assist a foreign intelligence service.
It is also alleged that they forced entry into a UK residence on 1 May.
The men spoke only to confirm their identities during their court appearance and were granted bail.
District Judge Louisa Cieciora imposed conditions including a 10pm to 5am curfew, reporting weekly to their local police station, no international travel and informing police of devices used to access the internet.
They are next due to appear at the Old Bailey on 24 May.
China, under which Hong Kong operates as a special administrative region, has refuted the allegations that the city's intelligence service was involved.
Hong Kong's government, meanwhile, said in a statement that it "demanded the UK government to provide full details of relevant information of the alleged matter concerned", adding that it was awaiting a response.
Police said eight men and a woman were arrested by counter-terrorism officers on 1 May in the Yorkshire area. The following day, a man was arrested in London and another man arrested in the Yorkshire area.
Seven men and the woman were released from custody on or before 10 May.
