China has reacted furiously to Britain's offer to open its doors to Hong Kongers fleeing a draconian new national security law, declaring the move illegal and vowing retaliation against the city's former colonial power.
Chinese officials claimed Thursday that the U.K. had no right to make its offer of residency and citizenship to potentially millions of eligible Hong Kongers, insisting the move would be a violation of agreements between the two countries, as well as international law.
"China strongly condemns this and reserves the right to take further measures. The British side will bear all the consequences," Chinese Foreign Ministry spokesman Zhao Lijian said at a briefing in Beijing.
In a statement, the ministry warned: "Any attempt seeking to undermine China's sovereignty, security and development interests is doomed to fail."
The comments came after British Prime Minister Boris Johnson said Wednesday that his government was changing its immigration laws to give a large group of Hong Kongers the right to live, work and eventually gain citizenship in the U.K., in response to the harsh new security law banning sedition, subversion and other broadly defined political crimes in the city.
The rights will be extended to holders of the British National (Overseas), or BNO, passport — a special category of British passport available to Hong Kongers born before the handover in 1997. About 350,000 Hong Kongers currently hold the passports, but around 3 million of the city’s 7.5 million people are eligible for them.
China's ambassador to the U.K., Liu Xiaoming, said Thursday that any changes to the existing rights for BNO passport holders — who were previously only allowed visa-free access to the U.K. for up to six months — would be a breach of existing agreements between the two countries.
He said "all Chinese compatriots residing in Hong Kong are Chinese nationals, whether or not" they held the BNO passport: "If the British side makes unilateral changes to the relevant practice, it will breach its own position and pledges as well as international law and basic norms governing international relations."
But Steve Tsang, director of the SOAS China Institute at the University of London, told VICE News that there was no basis to Beijing's claims that Britain's citizenship offer was illegal.
"The ambassador is wrong in declaring the UK Government has no right to introduce a policy for its nationals overseas," he said. "There is no international law that prohibits it. There is nothing in the Sino-British Joint Declaration that prohibits it either."
He said that while China technically could block BNO holders from fleeing to the U.K., it would be difficult to enforce unless China took radical steps, such as a complete travel ban on BNO holders.
"It will … require a blanket ban on them leaving Hong Kong,” he said. “It is easier said than done, unless a draconian approach is adopted.”
British Foreign Secretary Dominic Raab said Wednesday that the U.K. could do little to stop China if it acted to block Hong Kongers from fleeing to the UK, besides applying diplomatic pressure.
"Ultimately we need to be honest that we wouldn’t be able to force China to allow BNOs to come to the UK," he told ITV.
Australian Prime Minister Scott Morrison said Thursday that his government was also drawing up plans to take in fleeing Hong Kongers, describing the new law as “very concerning.”
Hong Kongers have already been arrested on national security related charges since the law went into effect on Tuesday, including a 15-year old girl who waved a Hong Kong independence flag.
The law has also prompted pro-democracy groups to disband, and activists to flee the country. On Thursday, high-profile youth activist and former lawmaker Nathan Law announced he had fled Hong Kong as a result of the new law, although he declined to say which country he had gone to.
This article originally appeared on VICE US.