https://en.wikipedia.org/wiki/British_National_(Overseas)
> Applicants were required to be British Dependent Territories citizens by a connection with Hong Kong.[30] While about 3.4 million people acquired the status,[41] 2.5 million non-BDTC residents (virtually all Chinese nationals) were ineligible.[42] Those ineligible who wished to register as BN(O)s were required to have been naturalised as Hong Kong-connected BDTCs by 31 March 1996. Acquiring Hong Kong BDTC status other than by birth was no longer possible after that date.[37]
No, they can't. BN(O) was created pretty much exactly for the purpose of allowing British Hong Kong citizens to retain their British passports without any sort of right of residency in the UK. The UK didn't want millions of foreign refugees with a claim to residency to appear on their doorstep any more than any other country would (have?)...
https://www.gov.uk/types-of-british-nationality/british-nati...
"you: are subject to immigration controls and do not have the automatic right to live or work in the UK"
I get it that people are mad that democracy is under attack in Hong Kong, but this drift into considering extreme reactions is getting ridiculous.