Chief Executive Leung Chun-ying, who took the unprecedented step of filing the lawsuit to have the pair disqualified, said the ­government’s next step would ­depend on whether the duo would appeal.

Sixtus Baggio Leung Chung-hang and Yau Wai-ching promptly vowed to appeal all the way to the city’s top court if necessary after the judge decided they had “declined” to take their oaths “faithfully and truthfully”.

They faced a dilemma in ­deciding whether to give up the legal battle and run for by- ­elections, or to fight their “enemies”, the Hong Kong government and Beijing, all the way to the Court of Final Appeal, he said. They chose to fight.

“We can take the risk – spending every penny and even going bankrupt – to stand up for the truth,” Baggio Leung said. “As popularly elected lawmakers, we have the duty to guard the established system of Hong Kong.”

The Youngspiration pair were widely condemned for using “Hong Kong is not China” banners and what sounded like a ­derogatory word for “China” with wartime connotations during their swearing-in ceremony on October 12.

At issue was whether Legco president Andrew Leung Kwan-yuen, who had already invalidated their oaths, had the power to give them a second chance to be sworn in.

But Beijing’s Basic Law interpretation last Monday pre-empting the court judgment.

Stressing the need to maintain national security and to keep pro-independence voices out of Hong Kong’s legislature, the Standing Committee of the National People’s Congress ruled that lawmakers must take their oaths “sincerely”, “accurately” and “completely”. A deliberate failure to do so would mean disqualification with no second chance.

While many in the legal sector were concerned that Hong Kong’s judicial independence had been harmed, Mr Justice Thomas Au Hing-cheung said “with or without the interpretation, the court would reach the same” conclusion as the government.

The judge, adopting a common law approach to the Oaths and Declarations Ordinance, said the localist pair “did not truthfully and faithfully intend to commit themselves” to the oath, as they “objectively clearly” did not recognise the principle of “one country, two systems”.

Au rejected the localists’ argument the court could not ­intervene in this case due to the doctrine of separation of powers – ruling that because oath-taking was a constitutional requirement over which the court was the “final arbiter”.

The judge said he “refrained” from commenting on whether Beijing’s ruling had, as some suggested, gone beyond the scope of “interpretation” because no parties argued about it substantively.

With an injunction barring the two from acting as lawmakers, Legco secretariat staff yesterday removed their name plates from their office doors. Legco president Andrew Leung Kwan-yuen said he would give them a few days to pack up.

Starry Lee Wai-King of the ­pro-establishment DAB party said the judgment was a “manifestation of fairness and justice” and she hoped it would settle matters. But Democrat James To Kun-sun said it showed Beijing’s interpretation was “unnecessary”.

Eric Cheung Tat-ming, principal law lecturer at the University of Hong Kong, said there would always be doubts in people’s minds as to whether the judge had been influenced by Beijing.