HONG KONG - Despite a national law protecting Hong Kong's autonomy and extensive Western-style freedoms, legal grey areas give China considerable room for manoeuvre in the city.
Simon Young, a professor at the University of Hong Kong law school, said that any mainland-orchestrated surveillance would be seen locally as a significant breach of the spirit of non-interference in Hong Kong affairs. But it would be hard to prove that this amounted to a violation of the territory's "one country, two systems" model.
Young said there are loopholes in the Basic Law under which Hong Kong is governed and scenarios in which Chinese officials could cite a need to protect national security. "It is going to be tough to win a one country, two systems argument," he said. "It would be more effective to consider the issue from the perspective of individual rights."
The Basic Law, frequently described as Hong Kong's mini-constitution, formally grants Hong Kong a "high degree of autonomy" and significantly limits the role of mainland operations in the city. But it does leave Beijing responsible for foreign affairs and defence.
The document notes the "inviolable" freedoms of Hong Kong residents, outlining freedoms of assembly, religion, movement and speech. Hong Kong also has its own laws, court system and a law enforcement regime entirely separate from the mainland.
In the 17 years since Hong Kong returned to Chinese sovereignty, local security officials have at times stressed that mainland law enforcers were strictly prohibited from taking action on their own in Hong Kong.
In answering a legislator's question earlier this month about whether there was any unauthorized monitoring of local protesters by mainland security officers in Hong Kong, Secretary for Security Lai Tung-kwok said Hong Kong residents' privacy and communications were protected by law.
"At present, no lawful channels are in place for law enforcement officers from other jurisdictions to conduct surveillance in Hong Kong," Lai told the Legislative Council.
The possibility of private citizens, such as retired police officers, running operations in Hong Kong alongside the mainland security apparatus further muddies the legal picture. Hong Kong's Bill of Rights and its laws governing covert surveillance bind only the actions of the local government and its officials. They don't apply to private citizens or mainland officials.
Pro-Beijing media in the city have frequently criticised local pro-democracy politicians for links to foreign groups, including US diplomats and the Catholic Church, which is well established in Hong Kong.
Both Western and Asian diplomats say they maintain a broad range of political and cultural ties in Hong Kong - routine contacts they say reflect their rights under the UN's Vienna Convention on Diplomatic Relations.