The reason this thought experiment doesn't really work is that it disregards a crucial piece of information that the CCP is an authoritarian regime, while the people of Hong Kong are liberal and democratic. People generally prefer to move from the former to the latter, and not from the latter to the former.
I think history is useful, but it doesn't really change the fact that the people of Hong Kong do not want authoritarianism. It should be irrelevant what some king in the Qing dynasty or British empire did. As common folk ourselves, we should be giving more value to the will of the people, than the will of people who buy and sell countries and its people as if it was private property. So, no, Hong Kong does not "belong" to CCP just because at some point it "belonged" to Qing dynasty.
Talking about people as if they are property of kings and rulers is just slavery at the level of groups.
In fact the US fought their bloodiest war over such issue...
I can't see how you imply UK and the US have any link on the topic.
I'm not sure what would happen if say 75% of a city wanted to leave the US because that has never happened and isn't very likely to.
The point is that the government is obviously finding ways to avoid a referendum because they obviously don't want Scottish independence.
Let's not be naive here.
The hard truth is that governments of any country on Earth favour self-determination in two cases: (1) when it does not apply to them, and (2) when they expect that they result will favour their interests. That's how geopolitics works. "People's interests" is just for PR.
How often does a country need to have a referendum on independence of regions that are so inclined to be said to support self determination? Also the polls leading up to 2014 were close enough that the result wasn't certain, yet the government went ahead.
I never said the UK would be happy with Scottish Independence. But if Independence was the clear preference of the people, the UK would let them go. The same can be said for the US and Puerto Rico, but not for China.
You said their position was "not to allow", which makes it sound like the Scottish people clearly want one but the UK won't allow it. That is not the case.