do you believe in the right of the living to vote for their own destiny.
Did we give the people of Hong Kong that right before we handed them over to China in 1999? I don't think so.
We didn't give the Chagossians that right either. It's just not something that we normally do.
If Argentina hadn't been so bullheaded in 1982 they probably would have been given a large degree of sovereignty over the Falklands by now. The Foreign Office wanted little to do with the place until the aggression of the '82 invasion by Galtieri. The Falkland islanders may or may not have been granted permission to emigrate to the UK as part of the deal. Probably not.
With Hong Kong only a small number of Hong Kongers were granted that right during/after the handover of that colony to the host nation. Most of the indigenous Hong Kong people were reasonably happy with the status quo and would have been happy to remain a British colony, but the UK government overruled their preferences and did a deal with Beijing which took little account of the feelings of the people of the colony.
Edited to add another case example:
Before we handed over the Palestine to the Israelites, did we canvass Palestinian popular opinion? I don't think so. We simply robbed them of their land and of their independence without regard for Palestinian rights. Their opinions simply didn't matter to London.