The UK will introduce a new visa at the end of January that will give 5.4 million Hong Kong residents - a staggering 70% of the territory's population - the right to come and live in the UK, and eventually become citizens.
It is making this "generous" offer to residents of its former colony because it believes China is undermining Hong Kong's rights and freedoms.
Not everyone will come. Some of those eligible to leave have expressed their determination to stay and continue the fight for democracy.
In the end, Britain estimates that about 300,000 will take up the visa offer over the next five years.
But some are so keen to leave that they are already in the UK, including Andy Li and his wife Teri Wong.
The couple moved to the city of York with their daughter Gudelia and son Paul in October, shortly after Britain announced it was planning to launch the new visa scheme.
They made the move primarily for their children.
"We feel that the things we treasure about Hong Kong - our core values - are fading over time," said Mr Li.
"So we decided we needed to provide a better opportunity for our children, not only for their education, but also for their futures."
For Mr Li, Britain provides the kind of society - the rule of law, freedom of speech, democratic elections - that he longed for in Hong Kong.
Mrs Wong said she wanted her children to be able to say what they wanted at school, not like in Hong Kong, where they had to be careful. "That's not the life we want them to have," she said.
Britain has allowed Hong Kong residents like Mr Li and his family to move to the UK even before the new visa comes into force.
But from 31 January, they can begin the process of applying for citizenship, which will take six years.
In the meantime, they will have to fund themselves, although they will be able to get healthcare and have their children educated.
Gudelia, who is 14, and Paul, 11, have already found a new school.
Mr Li continues to work remotely for a Chinese electronics company based in Shenzhen, the Chinese city just over the border from Hong Kong.
The family are excited about their new life, but others have arrived with less of a sense of starting something good as fleeing something bad.
One person who did not want to be identified came to Britain recently after taking part in pro-democracy protests in Hong Kong in 2019.
"I fear for the safety and security of the friends and family who decided to stay behind," the 23-year-old told the BBC.
"And I am afraid I will also become a target for the Hong Kong authorities because of my active participation in the protests."
But even this person has hope for a better life: "Being granted a chance to live here is a dream come true."
Since the UK handed back its former colony 23 years ago, relatively few of the territory's residents - less than 16,000 - have become British citizens.
That is certain to change, partly because the new visa scheme appears to offer few hurdles for the millions eligible to apply.
"I had clients applying to Canada, Australia and Taiwan who suspended their applications and now want to go to the UK," said Andrew Lo, a Hong Kong immigration adviser.
Another consultant in the territory, Colin Bloomfield, said the visa provisions did appear generous, although he said Britain might add more requirements that would make it harder to move.
The scheme is open to Hong Kong residents who claimed British National (Overseas), or BNO, status before the handover in 1997. A total of 2.9 million people registered and so can apply for the new visa.
Their dependants - an additional two-and-a-half million people - are also eligible to travel with them.
Teri Wong is the only person in her family who has registered for BNO status, but she has been allowed to bring her husband, who was born in China, and their two children to Britain with her.
'Why should I leave?'
Although the British government admits that as many as one million people could apply for the visa over the next five years, it thinks only a few hundred thousand will actually do so.
It believes most people will choose to remain in Hong Kong.
Some residents will not want to leave behind elderly parents or learn a new language; the British weather is certain to dissuade others.
Many do not want to abandon the territory to its fate.
"There is a certain number of people who do not want to leave, particularly the young. They would rather die in Hong Kong," said Mr Lo.
"I have a lot of clients who fight with their kids because the children don't want to emigrate. They say: 'Why should I leave? I should try my best to change this place'."
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There is also the difficulty of finding work in Britain, as the country tries to recover from the coronavirus pandemic, and Brexit.
And if enough come, new arrivals could face resentment from British people who oppose too much immigration.
"In the cold light of day, many will decide to stay in Hong Kong," said Mr Bloomfield, whose company is called British Connections.
Regardless of how many apply, the British government said it had no choice but to offer Hong Kong people an escape route.
"This is not a question of numbers," said a Home Office spokesperson.
"The government is committed to giving British National (Overseas) citizens in Hong Kong a choice to come to the UK, fulfilling our historic commitment to them."
Britain believes that when China imposed its national security law on Hong Kong earlier this year, it breached the terms of the handover agreement signed by the two countries.
The space for expressing opinions that the Chinese government does not like has certainly narrowed since the law came into effect in July.
In the end, the number of Hong Kong residents emigrating to Britain might depend on how much more Beijing decides to squeeze.