Boris Johnson has said he will have 'no choice' but to offer the people of Hong Kong citizenship if China erodes human rights in the former British colony.
The Prime Minister said last night that a proposed new national security law in Hong Kong would 'dramatically erode its autonomy' and breach the terms of its treaty with the UK.
Mr Johnson said he would 'willingly' bring in one of the 'biggest changes in our visa system in British history' as an 'alternative' to Chinese repression.
Beijing's push to impose its will in the former British colony has stoked worry about its future.
It has prompted Britain to offer refuge to almost three million Hong Kong residents eligible for a British National Overseas passport.
Boris Johnson said he would 'willingly' bring in one of the 'biggest changes in our visa system in British history' as an 'alternative' to Chinese repression
A pro-democracy protester waves a British colonial flag during a rally at a shopping mall in the Central district in Hong Kong on Monday
Writing in the Times, Mr Johnson said: 'Britain would then have no choice but to uphold our profound ties of history and friendship with the people of Hong Kong.
'Today, about 350,000 of the territory's people hold British National (Overseas) passports and another 2.5million would be eligible to apply for them.' Currently the passports allow visa-free access to the UK for up to six months.
He added: 'If China imposes its national security law, the British government will change our immigration rules and allow any holder of these passports from Hong Kong to come to the UK for a renewable period of 12 months and be given further immigration rights, including the right to work, which could place them on a route to citizenship.
'This would amount to one of the biggest changes in our visa system in history.
'If it proves necessary, the British government will take this step and take it willingly.
'Many people in Hong Kong fear their way of life, which China pledged to uphold, is under threat.
'If China proceeds to justify their fears then Britain could not in good conscience shrug our shoulder and walk away; instead we will honour our obligations and provide an alternative.' It is understood the people of Hong Kong will be offered a route into Britain only after the publication of full details of the proposed laws, expected this month.
A protester holds up the British National (Overseas) passports in a shopping mall during a protest against China's national security legislation for Hong Kong
The BNO passport was created for Hong Kong people before Britain returned the territory to Chinese rule in 1997.
Though they are British passports that allow a holder to visit Britain for six months, they do not come with an automatic right to live and work there.
But the Foreign Secretary has said the six-month limit could be removed if, as is expected, China imposes its draconian legislation on the city.
The pledge has seen people who held BNO passports rush to replace them.
Mother of two Ming Wong, 39, was one of those to re-apply for her lost passport.
'I started filling out the applications in December after the protests, but it's the national security legislation now that really prompted me to finish the process,' Wong said.
Her husband, brother and parents are also applying, she said.
According to figures obtained by the Mingpao newspaper from the British Passport Office, BNO renewal applications increased in the second half of last year, amid sometimes violent anti-government protests, with the number totalling more than 120,000 in 2019 compared with about 14,000 in 2017 and 2018.
Beijing's push to impose its will in the former British colony has stoked worry about its future
Immigration consultants have reported a rush of enquiries about moving away from Hong Kong since China's announcement on May 21.
'Last week alone, the number of enquiries surged to about 100 a day,' said Swing Wong, a director the Midland immigration consultancy, from about 50 a day earlier this year.
'Most people who enquire about the UK think it would be a safety net for their children,' said Ivan Yam, director of immigration consultant Golden Emperor Properties.
Mr Raab yesterday told the House of Commons there was still time for China to withdraw a bill that Beijing says is necessary to protect itself.
When passed, it will allow China to put its own security measures, such as secret police and arbitary detention of critics, in place in Hong Kong, destroying the 'one country, two systems' promise that is due to run until 2047.
Mr Raab said: 'If China is willing to interfere on political and autonomy grounds, it is also likely to pose a longer term threat to the economic prosperty and economic model that Hong Kong reflects and embodies.
'The sad reality is that if China continues down this track, it will be strangling what has long been the jewel in the economic crown.
'There is still an opportunity for China to step back,' he said but added: 'We think that it is unlikely that will happen.'