Britain's offer increases pressure on Australia to also offer residency to those fleeing Beijing's crackdown,something Foreign Secretary Dominic Raab has previously revealed he asked of his Australian counterpart Marise Payne and other Five Eyes ministers.
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Delivering a statement to the Commons following Johnson's comments,Raab hinted at possible action from the group.
"In reality,a large number of those who might be eligible will want to stay in Hong Kong,"Raab said.
"Others may go to countries in the region,but we have a historical responsibility and therefore we are making our position clear.
"I have also had a number of conversations with our international partners,particularly those with specific and close relationships with Hong Kong and who have large numbers of that community in their countries.
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"I would expect others to be looking very carefully at what they do."
Raab said under the"bespoke immigration route",eligible Hong Kongers would be offered the right to work and live in Britain for five years,after a further 12 months they will be eligible to apply for British citizenship. He promised the system would be streamlined and would be unlimited in capacity.
"The Foreign Secretary’s commitment to BNO passport holders is welcome,but it does not resolve the problem,"Labour's foreign spokeswoman Lisa Nandy said.
"I was deeply moved to see the young activists who bravely took to the streets to protest against this law,at considerable personal risk,"she said.
"The majority will not be covered by this scheme and must not[be] abandoned."
The undertaking by the British government came as thousands of protesters gathered downtown in Hong Kong for an annual rally marking the 23rd anniversary of the former British colony's handover to China in 1997.
Riot police used pepper spray to make arrests,while shops and one metro station closed.
"I'm scared of going to jail but for justice I have to come out today,I have to stand up,"said one 35-year-old man who gave his name as Seth.
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Crowds spilling out into the streets chanted"resist till the end"and"Hong Kong independence".
Police fired water cannon to chase them away and said they had made more than 300 arrests for illegal assembly and other offences,with nine involving suspected violations of the new law.
Earlier,police cited the law for the first time in confronting protesters.
"You are displaying flags or banners/chanting slogans/or conducting yourselves with an intent such as secession or subversion,which may constitute offences under the ... national security law,"police said in a message displayed on a purple banner.
The law will punish crimes of secession,subversion,terrorism and collusion with foreign forces with up to life in prison and officially set up mainland security agencies in Hong Kong for the first time,with powers beyond city laws.
With Reuters and Staff Reporters
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