I don't claim to be an expert historian in the area. These are memories from a vague interest in current events in those times. Wikipedia seems to support but I know that's not an end to the matter. If you have deeper information and links do please share.

The 1983 act is just before they announced the 1997 handover.

https://en.wikipedia.org/wiki/British_Overseas_Territories_c...

"At the time of nationality reclassification in 1983, the largest group of BDTCs (2.5 million people) was associated with Hong Kong. The deprivation of full passports and nationality rights for colonial residents was criticized for effectively codifying ethnicity as the deciding factor in determining what rights British subjects were entitled to, an impression confirmed by exceptions granted to the majority white residents of Gibraltar and – after the Falklands War – the Falkland Islands. The British government was particularly unwilling to grant full citizenship and immigration rights to Hongkongers, fearing a mass migration to the UK after the transfer of sovereignty to China in 1997."