Ever since the internet arrived in China in the mid-1990s, many have assumed that it poses an unanswerable threat to the sprawling system of political censorship that helps underpin the ruling Communist party’s power.

Such confidence was memorably summed up in 2000 by Bill Clinton, then US president, who predicted that liberty would spread unstoppably in the 21st century “by cell phone and cable modem”. “There’s no question China has been trying to crack down on the internet,” Mr Clinton said. “Good luck. That’s sort of like trying to nail Jell-O to the wall.”