Testifying as a prosecution witness for a third day, Au recalled before national security judges Andrew Chan Hing-wai, Alex Lee Wan-tang and Johnny Chan Jong-herng on how the unofficial Legislative Council primary election in 2020 was coordinated.

He said Tai had had met with many pro-democracy politicians to introduce his ideas to "proactively utilize" legislators' veto power. And if the administration did not act according to public opinion legislators could vote down the budget.

Au said no one challenged or even discussed Tai's advocacy on "proactively utilizing" legislators' veto power.

But in a meeting with New Territories East politicians in April 2020, localist Owen Chow Ka-shing asked Tai why he said only to "proactively utilize" the power but not "exercise" the rights.

Au said the discussion turned into an intense debate, but Tai insisted on his way of phrasing the matter.

Au believed Tai wanted to ensure his idea was flexible.

In another meeting with Kowloon West candidates, localist Sunny Cheung Kwan-yang, currently in self-exile, said he supported vetoing the budget, but Civil Human Rights Front convener Jimmy Sham Tsz-kit disagreed.

Cheung told Tai he had seen the Occupy Central founder's newspaper article on a 10-step "I die, you die" plot.

Au said: "When it was published I told [Tai] his idea was very mad."

After three meetings with Kowloon East pro-democrats, Au said Kwun Tong district council chairman Choy Chak-hung sent out the minutes of the meeting in a chat group on WhatsApp. Au said he remembered it said: "Proactively utilize Basic Law rights, veto the budget."

The high court judges asked if Au could provide a document for their reference, but Au said he did not have the minute as he did housecleaning on his phone every month.

Sixteen of 47 pro-democratic figures in the dock have pleaded not guilty to conspiracy to commit subversion between July 1, 2020 and January 7, 2021. Au and Tai are among the 31 who pleaded guilty.

The trial continues today.