From a woman waving a colonial-era flag in a shopping mall, to bakery staff selling cakes with protest symbols on them - dozens of Hongkongers have been reported to the police by one man for what he believes were national security violations.

“We’re in every corner of society, watching, to see if there is anything suspicious which could infringe on the national security law,” former banker Innes Tang tells the BBC World Service.

“If we find these things, we go and report it to the police.”

When the UK returned Hong Kong to China 28 years ago, internationally binding treaties guaranteed the city’s rights and freedoms for 50 years. But the national security law (NSL), imposed by Beijing a year after Hong Kong’s 2019 mass pro-democracy protests, has been criticised for scuttling free speech and press, and for ushering in a new culture of informing.