How China's plan to neuter Hong Kong opposition works

China's decision to overhaul Hong Kong's already limited election system is the latest measure aimed at snuffing out opposition to Beijing's rule after huge democracy protests swept the city.

Here's what the new measures are and what impact they will have:

The "reforms" unveiled on Tuesday are the most dramatic overhaul of Hong Kong's political system since the city was handed back to China by Britain in 1997.

Under a model dubbed "one country, two systems" China promised Hong Kong could keep certain freedoms and a level of legislative autonomy for 50 years.

The city was never a democracy — even though its Beijing-approved mini-constitution states that "universal suffrage" is an ultimate goal.

Instead, a carefully calibrated political system was created to ensure Beijing maintained control while maintaining a veneer of choice that allowed opposition voices to exist.

That system is now gone.

Sitting on top of everything will be a new powerful committee that will vet anyone standing for political office.

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Those deemed to be a national security threat or not adequately patriotic enough will be barred from standing for election or appointment.

Those who are rejected will not be able to challenge the decision in court.

Tam Yiu-Chung, Hong Kong's sole delegate on the Chinese body that passed the new law, revealed that the vetting committee will be created by authorities in Hong Kong and the city's new national security apparatus would have a say in who gets approved.

Even before this new law, barring Hong Kongers from political office because of their political views has become more commonplace in recent years.

But the new system dramatically expands the ideological vetting.

Alvin Cheung, a legal scholar at New York University's US-Asia Law Institute, said China's leaders have never really trusted Hong Kongers to vote the right way.

"From Beijing's perspective, the elimination of meaningful political participation is necessary," he told AFP.

Under the old system, Hong Kong's legislature had 70 seats, half of which were directly elected.

The rest were chosen by "functional constituencies" representing key industries and special interest groups that were largely pro-Beijing.

The city's "chief executive" leader, meanwhile, was chosen by a reliably 1,200-strong pro-Beijing panel known as the Election Committee.

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The new reforms expand the legislature's seats to 90.

Only 20 will be directly elected, down from 35.

The majority -- 40 -- will be chosen by the Election Committee (itself expanded to 1,500 members) and the remaining 30 will be chosen by the functional constituencies.

The result is a chamber where directly elected voices are slashed from half the seats, to less than a quarter.

"Pro-democracy groups are likely to have a very marginalised voice in the legislature, if even that," Chong Ja Ian, an associate professor on politics from the National University of Singapore, told AFP.

But the reforms don't stop there.

Under the "one country, two systems" arrangement, Hong Kong is supposed to make its own laws but Beijing has tired of using the city's legislature.

Much like last year's national security law, the election reforms passed on Tuesday were written directly in Beijing, bypassing Hong Kong's legislature entirely.

At the time the law was passed on Tuesday morning, Hong Kong's 7.5 million people still had no idea what it contained.

China has defended this method of legislating Hong Kong directly as necessary to counter national security threats and ensure only "staunch patriots" rule the city.

Hong Kong's legislature was a notoriously fractious place.

Relegated to a minority, Hong Kong's pro-democracy politicians tended to use filibustering and other procedural tactics to delay legislation.

Late last year, opposition politicians quit en masse after four of the colleagues were barred for being deemed national security threats.

Since then, government bills have breezed through unhindered by messy debates and questioning.

The new system is aimed at ensuring that smooth sailing continues.