Let’s put it in plain words: the people of Hong Kong haven’t defeated the proposed extradition law to China yet – we have only earned a small window to catch our breath. And so have the hardliners in the administration and the Chinese government.

Last Friday, thousands of protesters staged a sit-in in front of the police headquarters in Hong Kong. Most of the protesters were in their early 20s; many were still high school students. They chanted slogans, demanding the full withdrawal of the unpopular extradition bill, the dropping of riot charges against peaceful protesters, and justice for the victims of police brutality.

The protesters might be youthful, but they are mature enough to know the temporary concessions made by the government can be overturned in the twinkling of an eye. Beijing is hiding under the radar to avoid losing further popular support, but its plan to erode the autonomy and freedom of Hong Kong continues. We are certain that stricter social control from Beijing will be imposed on our liberal society under Xi Jinping’s iron-fisted rule. We know this because we are fully aware of Hong Kong’s recent history.

The first major pushback against Beijing’s intervention in the freedom of the region happened in 2003. Then, half a million people protested furiously against China’s attempt to use national security legislation to suffocate freedom of expression and the right to dissent. The Hong Kong government came under sustained pressure, and withdrew the controversial bill two months later. The protests led to the resignation of the chief executive of Hong Kong, and the opposition Democrats scored their best result ever in the elections that followed. It was a great triumph for everyone in the pro-democracy camp.

‘We are certain that stricter social control from Beijing will be imposed under Xi Jinping’s iron-fisted rule.’ Photograph: AP

But meanwhile, Beijing was secretly plotting a new, more intrusive Hong Kong policy. Legal scholars trusted by Beijing were deployed to research Hong Kong’s elections and its constitutional and bureaucratic system. In 2008, Cao Erbao, director of research of the Central Liaison Office, put together a team from mainland authorities to carry out this work.

A new relationship between Beijing and Hong Kong has since taken shape. Beijing has absolute control over Hong Kong’s affairs, weakening the very foundation of freedom, and stripping away the political neutrality of the bureaucracy, judicial independence and legislative scrutiny of the administration.

Beijing has effectively penetrated Hong Kong’s bureaucracy: more Beijing allies have been appointed into top positions, and civil servants are encouraged to participate in “exchange tours” hosted by Chinese government agencies. In 2017, for the first time since the handover, a high-ranking official from the central committee of the Communist party of China came to Hong Kong and gave a lecture on “Xi Jinping’s new era of Chinese socialism” to more than 240 officials.

This has set the stage for further abuses of executive power: electoral officers have disqualified and barred candidates from taking part in elections;pro-democracy lawmakers have been stripped of their seats. Last year, Victor Mallet, the Asia news editor of the Financial Times, found that his visa wasn’t going to be renewed, without any valid reason, in what was believed to be a de facto expulsion in retribution for inviting a political dissident to a talk hosted by the Foreign Correspondents’ Club.

Today young people are taking to the streets, putting their lives on the line because their fundamental rights are under threat. Beijing always escalates its social control in Hong Kong after significant grassroots protest. We may have stopped China from extraditing people for now, but the larger plot to erode and penetrate our rule of law and freedom remains.

We have learned the lessons of the past: pushing back an unpopular law is just the first step – next we need to institutionalise greater protections of our rights. This is why protesters are demanding officials must be held responsible for their abuse of power. Once we open a discussion on accountability, discussion on how to prevent the next crackdown on civil society will follow. The best defence is good offence.

• Joshua Wong is a Hong Kong pro-democracy campaigner and the secretary general of the Demosisto party; Johnson Yeung is a campaigner and human rights advocate in Hong Kong