Fourteen pro-democracy activists were convicted in Hong Kong’s biggest national security case on Thursday by a court which said their plan to effect change through an unofficial primary election would have undermined the government’s authority and created a constitutional crisis.

After a 2019 protest movement that filled the city’s streets with demonstrators, authorities have all but silenced dissent in Hong Kong through reduced public choice in elections, crackdowns on media and the Beijing-imposed security law under which the activists were convicted.

Those found guilty of conspiracy to commit subversion included former politicians Leung Kwok-hung, Lam Cheuk-ting, Helena Wong and Raymond Chan, and they could face up to life in prison when sentenced later.

The two defendants acquitted at West Kowloon Magistrates’ Courts were former district councillors Lee Yue-shun and Lawrence Lau, but the prosecution said it intends to appeal against the acquittals.

The activists were among 47 democracy advocates who were prosecuted in 2021 for their involvement in the election. Prosecutors had accused them of attempting to paralyze Hong Kong’s government and topple the city’s leader by securing the legislative majority necessary to indiscriminately veto budgets.

In a summary of the verdict distributed to media, the court said the election participants had declared they would “either actively use or use the power conferred on the (Legislative Council) by the (Basic Law) to veto the budgets”.

Under the Basic Law, the chief executive can dissolve the legislature if a budget cannot be passed but the leader would have to step down if the budget is again vetoed in the newly formed legislature.

In the full, 319-page verdict, the court also said if the plan to veto Bills would lead to the dissolution of the legislature, it meant “the implementation of any new government policies would be seriously hampered and essentially put to a halt”.

“The power and authority of both the Government and the Chief Executive would be greatly undermined,” the court said in the verdict. “In our view … that would create a constitutional crisis for Hong Kong.”

The judges concluded that “unlawful means” are not limited only to criminal acts, and that it was not necessary for the prosecution to prove the accused knew that the means to be used were “unlawful”.

Mr Lau, who was acquitted, told reporters he should not be the focus at the moment as other defendants in the case warrant the public’s concern and love.

He said if there is any “star” in the case, the judgment should be “the star” because it set out the logic and perspectives of the judges. “This is part of our rule of law,” he said.

The court acquitted Mr Lau after it found he had not mentioned vetoing the budget in his election campaign and the court was unable to conclude he had intended to subvert state power.

Mr Lee, the other defendant found not guilty, thanked the public for caring about the case over the past few years.

“I feel calm, as I have always been,” he said.

In an earlier Facebook post, he said Thursday was like a special graduation ceremony for him, though graduation is usually about sharing happiness with families and friends.

“This perhaps best reflects the common helplessness of our generation,” he had said in his post on Wednesday.

Mr Lee, like Mr Lau, was acquitted after the court found no evidence that he mentioned vetoing in an election forum, nor had he personally expressed his stance on using veto power to force the government to accede to protester demands.

While Mr Lee – then a member of the now-defunct Civic Party – had adopted a similar political platform as other party members, the court took into account that he was a latecomer to the party’s campaign for the primary election and that he would have had little choice but to adopt the platform used by others. Thus, the court said in the verdict it could not be sure he had intended to subvert state power.

The two men will be kept on bail, the court said.

Observers said the subversion case illustrates how the security law is being used to crush the political opposition following huge anti-government protests in 2019. But the Beijing and Hong Kong governments insisted the law has helped bring back stability to the city and that judicial independence is being protected.

When Britain handed Hong Kong back to China in 1997, Beijing promised to retain the city’s Western-style civil liberties for 50 years. However, since the introduction of the 2020 law, Hong Kong authorities have severely limited free speech and assembly under the rubric of maintaining national security. Many activists were arrested, silenced or forced into self-exile and dozens of civil society groups disbanded.

The activists prosecuted in the main case included legal scholar Benny Tai, former student leader Joshua Wong and a dozen former politicians including Leung and Claudia Mo.

Thirty-one of them, including Tai, Wong and Mo, pleaded guilty to the charge of conspiracy to commit subversion. They have a better chance of shorter jail terms and will be sentenced at a later date.

After Thursday’s verdicts for the 16 others who pleaded not guilty and underwent a non-jury trial, the court tentatively scheduled a mitigation hearing on June 25.

On Thursday, prior to the court hearing, Chan Po-ying, leader of pro-democracy political party League of Social Democrats, as well as three other LSD members, were arrested at court, according to a Facebook post by party member Figo Chan. Chan Po-ying is also the wife of Leung.

Reports by local media such as the South China Morning Post said those arrested had attempted to raise a yellow banner in protest as they walked on to court grounds but were stopped by police and escorted away.

Diplomats from the United States, Australia and Britain, along with dozens of residents, had waited outside the police-guarded court building to secure seats to hear the verdicts.

Former chairwoman of the Democratic Party Emily Lau was among those who turned up in support. She told reporters she was sad that so many had been locked up for more than three years, but declined to comment on the verdict.

Social worker Stanley Chang, a friend of one of the 16 defendants, said he arrived the site at 4am because he feared he could not get a seat. He said there were very few things supporters could do for them and that attending the hearing is a kind of company.

“I want to give some support for my friend and the faces I saw in news reports,” he said.

Maya Wang, acting China director at Human Rights Watch, said the convictions of 14 people “for their peaceful activism (show) utter contempt for both democratic political processes and the rule of law.”

“All Hong Kong people wanted was a chance to freely elect their government. Democracy is not a crime, regardless of what the Chinese government and its handpicked Hong Kong court may say,” she added.

Sarah Brooks, of rights group Amnesty International, described the mass convictions as “unprecedented” and said it is the “most ruthless illustration yet of how Hong Kong’s National Security Law is weaponised to silence dissent”.

“These convictions also send a chilling message to anyone else in Hong Kong who opposes the actions of the government, namely: stay quiet, or face jail,” she said.

The unofficial primary in June 2020 was meant to shortlist pro-democracy candidates who would then run in the official election. It drew an unexpectedly high turnout of 610,000 voters, over 13% of the city’s registered electorate.

The pro-democracy camp at that time hoped they could secure a legislative majority, which would allow them to press for the 2019 protest demands, including greater police accountability and democratic elections for the city leader.

But the government postponed the legislative election that would have followed the primary, citing public health risks during the coronavirus pandemic. The electoral laws were later overhauled, effectively increasing the number of pro-Beijing lawmakers in the legislature.