Mr Justice Andrew Chan Hing-wing told West Kowloon Court the case involved a “very lengthy and premeditated” plan to violate the security legislation.

“That’s the beginning of a chain reaction. You cannot simply artificially divide the whole thing into two,” the judge said.

Mr Justice Alex Lee Wan-tang noted Tai had advised a fellow organiser to donate HK$1 million to the Hong Kong Public Opinion Research Institute after the primary was held to conduct regular opinion polls and “exert pressure on some of the candidates” who might decide not to follow through with the conspiracy.

Beijing has imposed a three-tier system in classifying offenders found guilty of subversion.

Principal offenders or those committing crimes of a “grave nature” can face life imprisonment or be jailed for at least 10 years.

Those deemed to have “actively” participated in the offence can be sentenced to between three and 10 years.

Other participants can face a maximum of three years in jail, short-term detention or restrictions on movement.

Tai’s counsel on Tuesday asked the judges to place the former law professor in the lowest tier and sentence him to two years in jail after considering mitigating circumstances, including his timely guilty plea.

But the prosecution is seeking a minimum 10-year term for those who organised the primary, saying a leader such as Tai should be regarded as a principal offender as a matter of “common sense”.

Mr Justice Johnny Chan Jong-herng on Wednesday challenged the defence’s assertion that Tai was not the crime’s mastermind.

“The scheme is to find a majority of storm troopers to implement the scheme of indiscriminately vetoing the budgets. We are trying to find the Darth Vader of the whole scheme,” he said, referring to the main antagonists of the Star Wars franchise.

But Stewart Wong Kai-ming SC, for Tai, stressed his client had no control over the election and did not offer any direction to the opposition camp after the primary.

Wong said Tai had always been an advocate for non-violence and did not intend to instigate “complete chaos” in Hong Kong.

He warned against applying the security law retrospectively to punish his client for promoting the primary before the legislation was in place, including in an April 2020 article where he outlined a 10-step road map to achieve “real mutual destruction”.

Wong referred to Tai’s own mitigation letter, in which the scholar explained the road map was merely an application of game theory to predict the development of future events.

Tai said one should never take Hong Kong’s constitutional documents as a “crystal ball” and believed democracy was guaranteed to happen.

Wong argued: “It would be unfair for you, for this court, to attribute a motive of a person, when he was writing an article as part of his lifelong game theory advocate, to say that he must be intending, advocating, encouraging or inciting violence.”

Three other letters submitted on Tai’s behalf included two from law professor Albert Chen Hung-yee and lecturer Eric Cheung Tat-ming, his former colleagues at the University of Hong Kong.

Both scholars highlighted Tai’s “significant” contribution to academia and his “honest and genuine” belief, albeit mistaken, that what he did was lawful at the time.

A third letter, penned by pastor Patrick So, detailed Tai’s contribution to the church and the heartfelt concerns he had for violent clashes between police and students during the 2014 Occupy protests.

The court also heard pleas of mitigation from lawyers representing three other primary organisers, Au Nok-hin, Andrew Chiu Ka-yin and Ben Chung Kam-lun.

Their lawyers asked for extra reductions in their sentences for their guilty pleas and assistance rendered to the authorities by testifying for the prosecution in the 118-day trial.

They also indicated a neutral stance in an earlier debate over whether the tough sentencing regime of the security law was applicable in the present case.

Counsel for a fifth defendant, Gordon Ng Ching-hang, asked for leniency on the basis of his “ancillary” role in the scheme.

But Justice Lee said Ng had called on voters to avoid candidates who did not wish to be bound by the primary’s result to ensure its success. He took a risk breaking the law, so he had to bear the consequences, the judge added.

The court ruled last month that the unofficial poll was part of an opposition scheme to trigger a constitutional crisis through the indiscriminate use of lawmakers’ power to veto government budgets and force the chief executive to step down.

The three judges, hand-picked by the chief executive to handle national security proceedings, will hear pleas for lesser sentences from the remaining 40 defendants in groups according to their polling districts over the next two months.