It was premature for a Hong Kong court to disqualify two lawmakers for insulting China in their swearing-in oaths, when the legislature's president himself had yet to rule on the matter, lawyers have argued.

Appealing against the Hong Kong High Court's decision to bar lawmakers Sixtus Leung and Yau Wai Ching from the legislature, the duo's lawyers referred to the separation of powers enshrined in the city's common law jurisdiction and called for non-intervention by the court.

But the three appeal judges disagreed.

They noted that the Basic Law, or Hong Kong's mini-Constitution, is superior to common law principles such as non-intervention.

"The court has to intervene because the Basic Law is supreme. Never mind any common law principles. The Basic Law trumps the common law, I am afraid," said Justice Andrew Cheung.

As a former British colony, Hong Kong had adopted common law traditions where legal principles laid down by judges are binding on future cases.

Last week, High Court judge Thomas Au ruled that Mr Leung, 30, and Ms Yau, 25, had declined to take their swearing-in oaths on Oct 12 when they pronounced China as "Cheena" in a derogatory manner and displayed a banner that said "Hong Kong is not China".

Justice Au said the pair had "refused to pledge allegiance to the Hong Kong Special Administrative Region as an inalienable part of (China)" and should thus be disqualified from the legislature.

The duo from the pro-independence Youngspiration party went on to appeal against the ruling, which was in line with a controversial Beijing ruling issued earlier stipulating that lawmakers should take their oaths "sincerely".

Beijing's move to interpret the Basic Law sparked fears of an erosion of the city's autonomy, which led to massive street protests in Hong Kong earlier this month.

Yesterday, in a courtroom packed with journalists and members of the public, Justice Cheung said the Basic Law interpretation by Beijing "cannot be avoided".

The three appeal judges called on the defendants' lawyers to address Beijing's interpretation of Article 104 of the Basic Law, which states that lawmakers need to swear allegiance to Hong Kong as part of China.

Mr Hectar Pun Hei, who represents Mr Leung, said the interpretation was an expansion of the Basic Law and amounted to changing the mini-Constitution.

Senior Counsel Philip Dykes, who represents Ms Yau, said the court should intervene only when the oath administrator refused to administer the oath. He added that neither the president nor the clerk had made such a decision.

Yesterday, after a special meeting to discuss administrative matters, the Legco president told reporters that Mr Leung and Ms Yau each needed to return HK$930,000 (S$172,000) to the Legco.

This was for the salaries that they had drawn and the money given to help them with expenses such as buying computers, tables and chairs to set up their office.

In an interview with The Straits Times last week, the pair said they intend to counter the demands by the president.

"Theoretically, other than our salaries, all the other expenses are valid and accounted for," said Mr Leung.

"This is another legal matter that we will have to attend to after the appeal," he added.

The appeal hearing will be concluded today.