The Hong Kong government's decision this month to use emergency laws for the first time in 52 years was very different to the way the same laws were last used. The change in tactics is telling.

In 1967, Mao Zedong's Cultural Revolution spilled across the border from mainland China into the British colony. Chinese Communist Party activists led riots and bombings that killed 51 people and injured 848 more. The British governor, David Trench, confronted the unrest very directly. His emergency ordinances gave him the power to shut down newspapers, ban any speech considered provocative, raid and order shut any premises including schools, seize weapons, conduct secret trials, require people to give names and ID to the police on demand, and, most controversially, to detain and deport suspects.

Why was that the most controversial? Because anyone could be detained, even if they weren't actually breaking a law, according to a 2011 study by Ray Yep of the City University of Hong Kong. Once their jail terms were served, they could be summarily deported if they weren't British citizens. The governor called in helicopters from the Royal Navy to help conduct police raids. These measures worked.

But this time, when Hong Kong's Beijing-appointed chief executive, Carrie Lam, invoked emergency laws on October 4, it was to impose only one measure – to ban face masks. Her explanation: "We believe the new law will create a deterrent effect against masked violent protesters and rioters, and will assist the police in its law enforcement." How, exactly, she didn't say.