Aragon starts work on Monday as an estate agent in London, focused on finding clients who want to move to Britain’s capital from his home city of Hong Kong, a move he made himself four months ago.

His job is one of the first created by a new visa scheme that opens today, giving millions of Hong Kong residents the right to move to Britain and eventually seek citizenship, in response to a Chinese government crackdown in the city.

The Home Office estimates that more than 300,000 people will take up that offer over the next five years, seeking to escape a city whose future has been transformed by a draconian new security law.

When that law was passed in June last year, effectively ending Hong Kong’s limited autonomy and civil rights protection, Boris Johnson said it broke the terms of the 1997 handover from British colonial rule. The prime minister responded with a “path to citizenship”, open to more than 5 million Hong Kong residents, which has been angrily denounced by Beijing. Anyone with a British national overseas (BNO) passport, and their dependants, is eligible to move to the UK.

The scheme was what brought Aragon, who asked that his surname not be used, to the UK, after the pandemic thwarted his search for jobs in Canada or Australia. In September he took his life savings and flew to the UK, a country he had never visited before but now calls home. He did not have a job or accommodation lined up, but worried that if he stayed any longer in Hong Kong it might become impossible to leave. There were rumours about the government imposing exit permits.

“I am not exactly a frontline protester but I am radical enough,” he said. “I thought it was better to leave before it was too late.”

China has since said it will not recognise BNO passports, and although most in the city have other documents they can fly on, it is a symptom of Beijing’s anger.

One reason for China’s frustration may be the obvious appeal of Johnson’s offer. A large and rapid influx of people from Hong Kong is likely to be a financial boon to a Britain battered by Covid-19 and the end of the Brexit transition period.That would be a financial blow and a political embarrassment for China. Bank of America estimated in a recent report that departing Hong Kong residents could trigger capital outflows of HK$280bn (£26bn) this year alone, as people sell property and withdraw pension funds. Government figures put the “net benefit” for the UK at between £2.4bn and £2.9bn.

New arrivals will have to support themselves but will be able to access schools and the NHS, after paying the £624 annual immigration surcharge.

But activist groups are warning that the government needs to do more to prepare for the new arrivals, particularly given a spike in hate crime against people of East Asian heritage since the start of the pandemic.

Hong Kong Watch and 10 other campaign groups and charities wrote to the government this week urging them to step up work to support both the new arrivals and local authorities who will help them settle in. “There does not yet appear to be a meaningful plan to ensure that the new arrivals properly integrate,” says the letter, which calls for a cross-government working group. “We must learn from past mistakes and put the resources in place to ensure a warm welcome.”

Areas for consideration range from school capacity to language classes, and psychological support for those traumatised by 18 months of often violent upheaval in Hong Kong. Professionals, it says, will need guidance on updating or transferring qualifications, and a publicity campaign to ensure that BNO status is widely recognised would help them access everything from bank accounts to rental contracts.

Hong Kong Watch policy director Johnny Patterson said the pandemic may have bought a little more time to prepare, with anecdotal reports that some are delaying moving when Britain is in its third lockdown.

But after waves of mass arrests in Hong Kong, there are still many who feel they can’t afford to wait, said Simon Cheng, a former British consulate employee-turned-campaigner. “They fear if they do not go now, there will be no chance [to leave]. But the UK is currently in a deep problem of the pandemic, so they feel very confused,” he said, adding that there were widespread rumours about officials possibly moving to block departures.

“For most of them, the fear in Hong Kong would outweigh fear of the pandemic in the UK. They just really want to get a ticket out, in case Beijing moves forward [with exit controls].”

Among those who are taking their chances in lockdown Britain is Samson Chan, who noticed in December that he was being followed. He had worked as personal assistant to Ted Hui – a pro-democracy politician who is also now in exile – and decided to fly out earlier this month.

He speaks little English, and is not sure what work he will find once his residency is confirmed, but is glad to have escaped. “I don’t dare think about the future – that is very uncertain for everyone. I’m just focused on surviving.”

One bright spot is the network of pro-democracy supporters that have contacted him. “I don’t feel alone: I have lots of new friends in the UK,” he says, though lockdown means they are largely online friendships for now.

The foreign office worked hard to get the scheme up and running within months, with careful attention to security details.

The first arrivals, like Chan, were allowed to come to the UK on a different visa and apply for the BNO scheme once here. From February, those still in Hong Kong will be able to apply through an app, avoiding a trip to the UK consulate, where they might be monitored by security officials.

But there appears to have been less government focus on integration in the UK. No single official has been tasked with coordinating such issues. A Home Office spokesman said work was under way across government, and that local authorities had been updated. “We will be communicating further with those areas which may see higher numbers arriving to support their planning,” he added.

Popular destinations are likely to include Sale in Greater Manchester – for its good schools, reasonable house prices and proximity to Manchester United – Birmingham, Bristol, Milton Keynes and, of course, London.

Civil groups and campaigners have also set up a raft of grassroots support initiatives. Musician Winston Marshall, from Mumford and Sons, has created a buddy system to pair new arrivals with locals.

Campaigner Krish Kandiah has set up a one-stop online site to help with welcome and practicalities. He recently hosted a meeting between home secretary Priti Patel and some of the first arrivals from Hong Kong.

“My mum and dad moved here from India and Malaysia, and the stories I grew up with were that they weren’t very well welcomed. There was a lot of racism and xenophobia,” he said. “We have such a lot of people coming so quickly at a really difficult time. There are perhaps ways that people could see this mass immigration negatively. And so I want to make sure that we see the benefits to the nation, but also offer people all the welcome and support they need.”