A jailed university student who pleaded guilty to inciting secession in Hong Kong lost his bid to reduce his five-year sentence in a court ruling on Tuesday that is expected to set the bar for other cases brought under the national security law imposed by Beijing.

Lui Sai-yu pleaded guilty in April 2022 and admitted that content on a Telegram channel he administered incited others to separate Hong Kong from China or alter the legal status of the city unlawfully.

But his guilty plea did not get him a one-third reduction in the length of his imprisonment – as in many other cases under Hong Kong’s common law system – because the security law imposed minimum jail terms for serious offences.

Lui is one of some 260 people who were arrested under the security law as Beijing tried to crush dissidents following the massive protests in 2019.

The top court’s ruling on his appeal may guide sentencing in other national security cases, including for the city’s most prominent democracy leaders who also pleaded guilty.

The judges unanimously dismissed Lui’s appeal and ruled that the minimum penalty of five years is mandatory for those committing serious offenses in relation to secession as stipulated by the security law.

In sentencing him last year, a judge at a lower court originally planned to jail Lui for 44 months after giving him a one-third sentence reduction due to his guilty plea.

But she amended the sentence after the prosecution argued that the crime Lui committed was of a serious nature and therefore the minimum penalty should be five years.

Lui appealed against the decision but lost.

Eric Lai, a visiting researcher from King’s College London’s School of Law, said local laws under the city’s common law system do not usually set out minimum sentences in accordance with the seriousness of the case. That is more commonly seen in Chinese laws.

He said the latest ruling reaffirms the overriding power of the security law.

Lui was not a prominent pro-democracy activist. He was the fourth person jailed under the sweeping security law. He was studying civil engineering when he was first arrested in September 2020.

According to a previous judgment, his Telegram channel carried messages containing slogans often chanted by protesters during the 2019 demonstrations in the city.

The protests waned with the arrests and exiles of democracy activists, the Covid-19 pandemic and the security law.

Observers expect Tuesday’s judgment to guide other cases, including the future sentencing for 31 of the 47 activists who pleaded guilty to the subversion charges for their alleged involvement in an unofficial primary election in 2020. Those activists included former student leader Joshua Wong.

Critics say the freedoms promised to the former British colony when it returned to Chinese rule in 1997 have greatly declined after the enactment of the law. But the Hong Kong government praised it for restoring stability.