Two former opposition lawmakers are facing up to five years in prison after admitting to their roles in an unauthorised demonstration against the now-withdrawn extradition bill in Hong Kong more than a year ago.

Au Nok-hin and Leung Yiu-chung had their bail extended until sentencing following their guilty pleas on Tuesday at West Kowloon Court, where their District Court trial was held to accommodate the large number of journalists and supporters in attendance.

Seven other co-defendants, including media tycoon Jimmy Lai Chee-ying, are set to dispute the legality of their prosecution in a two-week trial over the same 2019 protest, the outcome of which could impact cases involving five other unauthorised assemblies. It will be the first trial arising from an unauthorised assembly in which the defence contests the constitutionality of the offence.

A group of former opposition lawmakers and activists will soon stand trial over their alleged roles in an unauthorised 2019 anti-government protest.

The trial centres on a demonstration in Causeway Bay on August 18, 2019, when protesters defied police and turned an approved assembly inside Victoria Park into an illegal march to Central.

The seven who have pleaded not guilty include Lai and six former opposition lawmakers: Martin Lee Chu-ming, “Long Hair” Leung Kwok-hung, Lee Cheuk-yan, Albert Ho Chun-yan, Cyd Ho Sau-lan and Margaret Ng Ngoi-yee.

All nine defendants were jointly charged with two offences under the Public Order Ordinance: organising an unauthorised assembly and knowingly taking part in an unauthorised assembly. Both charges carry a maximum jail sentence of five years.

On Tuesday, Au pleaded guilty to both charges while Leung admitted to knowingly taking part in an unauthorised assembly. The prosecution agreed not to press ahead with the other charge against Leung.

Reading out the case against the pair, prosecuting counsel-on-fiat Priscilia Lam Tsz-ying said police had granted protest organiser Civil Human Rights Front the right to hold the August assembly at Victoria Park.

But the force declined to approve either a procession from the park to Chater Road pedestrian areas or a subsequent assembly there “in the interest of public safety, public order, and the protection of rights and freedom of others”. That decision was upheld by an independent appeal panel under the Security Bureau on August 16.

At a press conference the next day, four of the defendants – Au, Lee Cheuk-yan, Ng and Leung Kwok-hung – and representatives of the front, detailed plans to hold a “water-flow assembly”.

The arrangement called for a group of opposition lawmakers to lead protesters out of the park and towards designated locations, particularly railway stations – ostensibly to make room for participants outside the park to join the rally.

But Lam said that was simply an excuse for the accused to lead a de facto march, disregarding their duty to assist police in ensuring participants obeyed the law.

The nine defendants eventually led a procession of thousands from Causeway Bay to Central on the afternoon of August 18, causing serious disruption to traffic on Hong Kong Island, the prosecutor continued.

The court heard that all the defendants but Lee Cheuk-yan, who was spearheading the march from the front, held a large banner emblazoned with the slogan: “Stop police from plunging Hong Kong into chaos. Implement the five demands”.

Au, using a loudhailer, called for people to join the march and gave directions to participants to walk along the route that was earlier banned by police.

Lam said: “[Au] repeatedly told protesters they were at the head of the public procession. [He] used a loudhailer and repeatedly said: ‘We appeal to you to go to Victoria Park and jam pack Victoria Park.’”

The former lawmaker also led protesters in chanting the slogan: “I have the right of procession. Police permission is not required,” in an attempt to motivate and galvanise the crowd, the prosecutor added.

District Judge Amanda Woodcock provisionally scheduled the duo’s sentencing hearing for March 22, subject to change depending on the progress of the trial. The prosecution will open their case against the remaining defendants on Wednesday.