The Government is preparing for a 100 per cent increase in the number of Hong Kong citizens coming to Britain after Boris Johnson offered up to three million residents sanctuary.
The Prime Minister said in July that Hong Kong's freedoms were being violated by a new security law and those affected would be offered the chance to settle in the UK and ultimately apply for citizenship.
The Foreign Office estimated that 200,000 people would move from Hong Kong to the UK, but a leaked internal briefing paper warned of a "rapid rise in the issue of British National (Overseas) passports since June".
BN(O) passport holders in Hong Kong were granted special status in the 1980s but currently have restricted rights and are only entitled to visa-free access to the UK for six months.
Under the Government's plans, all BN(O)s and their dependents will be given the right to remain in the UK, including the right to work and study, for five years. They will be able to apply for settled status and, after a further year, seek citizenship.
In February, there were 349,881 BN(O) passport holders in Hong Kong. By August 2020, there were over 400,000 live passports in circulation and more than 200,000 passport applications waiting to be processed.
The document added: "The Home Office predicts the number of BN(O) passport holders is likely to rise to 733,000 by the end of 2020." This would amount to a rise of 110 per cent since February.
A Government spokesman said: "In recognition of our moral and historic commitment to British National (Overseas) citizens in Hong Kong, we will introduce a bespoke immigration route with a path to full British citizenship. A BN(O) passport is not required to apply."