Hong Kong is facing its most serious political crisis since the former British colony was returned to China in 1997. At issue is what kind of electoral system the “special administrative region” should have for the 2017 election of chief executive, the equivalent of mayor.

Under the so-called Basic Law, the city’s “mini-constitution”, Beijing has agreed that Hongkongers should be able to elect their leader by universal suffrage. But its idea of what that means differs substantially from what many in Hong Kong’s pro-democracy movement aspire to. It has ruled out popular nomination of candidates, all of whom must be screened by a nomination committee. It also says only candidates who “l(fā)ove China” should be eligible, a stipulation widely interpreted as meaning allegiance to the Communist party.

Over the past 10 days nearly 800,000 people, in a city of just over 7m, have taken part in a “referendum” on the type of democracy Hong Kong should implement. Voters chose between three proposals, each of which would allow some form of public nomination process. Beijing has reacted angrily. It called the exercise “illegal and invalid”, an odd thing to say about a process that claimed no legal status. This week, Hongkongers showed their displeasure by turning out in huge numbers for the annual July 1 pro-democracy demonstration. Occupy Central, a pro-democracy group, has pledged to bring the central district to a standstill if electoral proposals fail to meet what it calls international standards.