A West Kowloon court yesterday rejected a bid by activist Avery Ng Man-yuen and six co-defendants to permanently stay the proceedings over their alleged unlawful assembly during a 2016 protest.
They had disputed a prosecution refusal to fully disclose documents on the day's police operations.
But West Kowloon Magistrate Peony Wong Nga-yan said she saw no evidence of any unfairness or abuse of procedure.
Ng, chairman of the League of Social Democrats, and eight other defendants, including the six who made the application, were arrested last April after taking part in a protest at central government liaison office in Western district in November 2016, when protesters engaged in a four-hour standoff with police.
The group was protesting against Beijing's interpretation of the Basic Law that led eventually to localist lawmakers being disqualified over the way they took the oath of office.
Wong ruled the trial would start today.
She said ordering a stay of proceedings was a discretionary power that courts could use only in exceptional circumstances - for example, when a fair trial was no longer possible or an abuse-of-legal procedure had been made. But Wong said Ng's case did not fall into this category.
"The court has already demanded the prosecution make a certain degree of revelation after considering the defendant's right to defense and protection of the public interest," she said.
Part of the contents were hidden from four police documents submitted to court regarding their operations on the day of the protest.
Chief Secretary Matthew Cheung Kin-chung signed a certificate of exemption in approval and the court also agreed with the non-disclosure.
However, the defense had argued that the move would compromise the group's right to a fair trial.
"Shameful Beijing interpretation, shameful disqualification of lawmakers," Ng and other defendants yelled outside court yesterday.
It is expected that two of the nine - Demosisto members Derek Lam Shun-hin, 23, and Ivan Lam Long-yin, 22 - will plead guilty today. The two did not ask a for stay of proceedings.
The other defendants are LSD's Ng, 40; Chan Man-wai, 23; Dickson Chau Ka-faat, 25; Student Fight for Democracy member Sammy Ip Chi-hin, 27; Lo Tak-cheong, 22; former president of Lingnan University student union Cheng Pui-lun, 22; and People Power's Chow Shu-wing, 66.
The trial is expected to last 20 days, with 57 witnesses to be called.