Up to one million people from Hong Kong could emigrate to the UK in the next five years under new visa arrangements, according to official estimates.

Some 500,000 Hongkongers could arrive in the first year after the visa becomes available from January 31, estimations from Home Office officials suggest.

The findings are part of an impact assessment carried out by the department after plans were set out to allow British National (Overseas) (BNO) citizens and their relatives who live in Hong Kong to apply for visas to live and work in the UK.

Officials have stressed that these figures illustrate an extreme scenario, are at the high end of their estimations and may not be reached, particularly because there is a high degree of uncertainty over how many people will take up the offer given the coronavirus pandemic and other factors.

But there will be no quota on the number of people who apply for the visa.

The assessment also gives “central range” figures, anticipating between 123,000 and 153,700 people could arrive in the first year, with between 258,000 and 322,400 over five years.

At the lower end of the scale, the department estimates as few as 4,000 people could come to the UK in the first year, with up to 9,000 over five years.

The net impact from the arrivals could be between £2.4 billion and £2.9 billion in revenue to the UK over five years, with the majority coming from extra taxes being paid, according to the findings.

Earlier this year, the Home Office announced plans to help grant rights to BNOs who live in Hong Kong so they could come to live and work in the UK if they wanted to leave after.

The imposition of the national security law on Hong Kong marked a clear erosion of the rights and freedoms for the people of this city

It came after the UK suspended its extradition treaty with Hong Kong and slapped an arms embargo on the territory in response to China’s national security law.

Andrew Heyn, the British Consul-General to Hong Kong, said the UK was ready to welcome the people of Hong Kong. He added: “The imposition of the national security law on Hong Kong marked a clear erosion of the rights and freedoms for the people of this city.”

Around three million people are thought to be eligible for BNO status and there are around 366,000 passports in circulation.

Some 715,000 people moved to the UK in the year to March, according to the Office for National Statistics (ONS).

From January, BNOs and their immediate family can apply for 30-month or five-year visas to live, work and study in the UK and can seek British citizenship once they have been in the country for more than five years.

They will not need a job or a valid passport to apply. They can use an expired passport to provide their identity or the Home Office has pledged to help confirm the status of those without documentation.

Although applicants will be able to access healthcare and go to school, they will not initially have access to benefits and will need to prove they can support themselves financially for the first six months of their stay.

They also have to provide a tuberculosis test certificate and show a commitment to speaking English.

Criminal history will be taken into account but it is unclear how immigration officials will view convictions for participating in protests, which constitute breaking China’s national security laws.

Applicants will have to pay £250 per person for a five-year visa as well as the immigration health surcharge. If they wish to remain in the country permanently they will need to later pay a settlement fee of around £2,400.

It is unclear what support may be offered to applicants with financial difficulties but the Home Office said the cost is lower than for other UK visas.

While the upfront costs of the 30-month visa will be cheaper at £180 per person, it would have to be resubmitted for those keen to stay in the country after it expires.

Before January, people with a valid Hong Kong passport can turn up at the UK border and will be granted entry for six months. They can then apply for the new visas or any others as part of the immigration system where they meet the criteria.

This means young Hongkongers – who may not have an automatic right to move to the UK because they are too young to have BNO status – may be able to enter the UK without their parents and then apply for the youth mobility scheme or as skilled workers under the forthcoming points-based system instead, if eligible.