Apply in the UK
You must apply online for a British National (Overseas) visa.
Your permanent home must be in the UK, Channel Islands, Isle of Man or
Hong Kong.
Switch to a BNO visa
If you meet the eligibility requirements, you can apply to switch to a BNO visa if you’re already in the UK on a different UK visa.
https://www.gov.uk/british-national-overseas-bno-visa/apply-in-the-uk
因為我見BNO visa個pages都有提到我假設個種情況,當然我理解英國唔會鼓勵人咁做,但總會有依類情形
同埋事實係我入境個刻,我真係未確認自己是否要移民...