On the other hand, Jat Sew-tong SC, who acted for Legco president Andrew Leung Kwan-yuen, dismissed the nature of the government’s argument as “dubious”, cautioning the court against moves that would constitute “serious deprivation” of the pair’s constitutional rights.

Two legal provisions are at stake in the legal battle. Under Article 104 of the Basic Law, lawmakers assuming office should “swear to uphold the Basic Law of the Hong Kong Special Administrative Region of the People’s Republic of China” and swear allegiance to the HKSAR of the PRC.

Under section 21 of the Oaths and Declarations Ordinance, any lawmaker who “declines or neglects” to take an oath duly requested should either have his or her office vacated or be disqualified from the office.

Watch: pro-independence lawmakers battle Hong Kong leader in court

In the urgent court proceedings on Tuesday – which primarily dealt with, and quashed, the government’s request for an interim injunction against a new oath for the two – Mok offered a glimpse into the government’s main argument for reviewing Andrew Leung’s decision.

He said under the Basic Law provision, special attention should be given to the words “of the People’s Republic of China” after mentioning Hong Kong. The emphasis on national sovereignty, he added, reflected the spirit in the law which was betrayed by the acts of the two lawmakers.

“The members not only neglected to [take the oath] but ... they want to exhibit to the world [that] ‘I do not accept these principles’,” Mok told the court.

University of Hong Kong legal scholar Eric Cheung Tat-ming lamented that the argument was “a far cry” from his understanding of the Basic Law – the mini-constitution that gives Hong Kong special status distinct from the mainland.

The arguments, he added, “were familiar in the sense they bore resemblance to the editorial views of Ta Kung Pao and Wen Wei Po”, two of Hong Kong’s most pro-communist papers.

For pro-democracy lawmakers and academics, the government’s move was a threat to – if not violation of – the separation of powers.

HKU law professor Johannes Chan Man-mun said: “As the Legco president has already made a ruling ... the secretary for justice’s decision [to lodge a judicial review] is in contravention of separation of powers and appears to be based on political, rather than public, interests.”

But the justice secretary dismissed such worries.

“When the view of the legislature or the Legco president differs from that of the executive authorities, the most appropriate way is to submit the question to the court for adjudication,” Yuen said yesterday. “This is a practice that shows respect for the rule of law. Oath-taking is ... different from Legco’s own affairs.”

Ronny Tong Ka-wah, ex-lawmaker and former Bar Association chairman, agreed that if a lawmaker-elect failed to complete the oath-taking process, he or she could be considered disqualified. The decision rested with the judiciary rather than the legislature, he said.

The justice secretary said there was no need at this stage to start the hugely controversial option of seeking an intrepretation of the Basic Law by the National People’s Congress Standing Committee: “We understand the central authorities have the right to interpret provisions of the Basic Law but we consider the Hong Kong judiciary capable of handling the questions in the judicial processes we launched last night.”

There were strong protests in the legal sector when the Tung Chee-hwa administration sought Beijing’s constitutional interpretation that effectively overturned a right-of-abode decision by the city’s top court.

The Basic Law guarantees that Hong Kong’s judicial system enjoys the power of final adjudication – unless the NPC Standing Committee considers it necessary to interpret the law in cases that are the responsibility of the central government or concern the relationship between the central government and Hong Kong.

When government lawyers enter the courtroom again in two weeks, it will be far more than just another legal debate. It is a case that could trigger the unprecedented scenario of democratically elected lawmakers being disqualified – or unpredictable reactions from mainland officials wary of public office holders preaching secessionist agendas. Either way, the case sets the stage for uncertainty and public resentment.