HONG KONG (Reuters) - Dozens of pro-Beijing lawmakers walked out of the Hong Kong legislature on Wednesday to prevent the swearing-in of two pro-independence activists, setting the scene for a new constitutional crisis in the Chinese-controlled city.

Empty seats with China and Hong Kong flags are seen inside a chamber after pro-Beijing lawmakers staged a walk-out to stall legislator-elects Baggio Leung and Yau Wai-ching from swearing in at the Legislative Council in Hong Kong, China October 19, 2016. REUTERS/Bobby Yip

The topic of independence has long been taboo in the former British colony, now governed under the “one country, two systems” principle since its return to Communist Party-ruled China in 1997.

The government failed in an unprecedented legal attempt to halt the swearing-in of the two newly elected legislators, Baggio Leung, 30, and Yau Wai-ching, 25, late on Tuesday evening.

But High Court Judge Thomas Au did approve the government’s request for a judicial review of the case, which will take place early next month.

The pro-China lawmakers on Wednesday marched out of the Legislative Council chamber, leaving Chinese and Hong Kong flags in their place, to deprive it of a quorum.

Senior pro-establishment lawmaker Regina Ip said she generally disapproved of walk-outs, but the legislators had no option after the pair refused to apologize for “insulting our motherland”.

“This is a very exceptional case involving a fundamental principle which involves loyalty to your country and adherence to our oath of upholding the ... law,” she said.

Yau said it was the pro-establishment camp that needed to apologize as they were “the ones who really betrayed the Hong Kong people”.

New legislative president Andrew Leung, himself a pro-establishment figure, stood by his defiance of government efforts to ban Yau and Leung.

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“They are duly elected... and I have a constitutional duty to safeguard their rights to fulfil their duties as Legislative Council members,” he said.

He said he thought Hong Kong was still far from a constitutional crisis and said he had no regrets about his decision.

It is unclear when the swearing-in will now take place.

DEROGATORY JAPANESE SLANG

Yau and Leung sparked outrage from Hong Kong’s pro-Beijing establishment when their first oaths were rejected by legislative officials last week.

At the time, they pledged allegiance to the “Hong Kong nation” and displayed a banner declaring that “Hong Kong is not China”, using language some legislators portrayed as derogatory Japanese slang.

Leung and Yau are part of a new generation of Hong Kong activists determined to force issues of self-determination and independence on to the mainstream political agenda.

Street protests calling for full democracy for Hong Kong that blocked key arteries in 2014 presented Communist Party rulers in Beijing with one of their biggest political challenges in decades.

Outside the chamber, hundreds of pro-Beijing protesters thronged the grounds of the legislature, some carrying placards of the pair dressed in Japanese army uniforms that denounced them as “traitors” and “dogs”.

Others chanted that the pair must step down to protect China’s “dignity”.

The judicial review looms as a unprecedented constitutional battle in the free-wheeling global financial hub, testing its rule of law and the separation of powers between the government and legislative branch.

Some senior judges and government officials fear privately the issue could force Beijing to invoke rarely used to powers to re-interpret Hong Kong’s mini-constitution, or push through new laws.

Hong Kong’s Secretary of Justice, Rimsky Yuen, said his government launched its challenge without direction from Beijing and it would not seek any interpretation from the National People’s Congress.

“We have confidence that the issue can be resolved in the Hong Kong system.”

Regina Ip said it was a “high risk” legal action that the government may not completely win.

“The chief executive’s action last night was an... extreme measure to deal with what clearly (he) considers an extreme situation.”