> If the UK had really wanted to keep Hong Kong, could it have militarily defended it?

The Chinese would not have to have fired a shot to make HK surrender. HK was then a city with more than 6 million citizens, which was entirely dependent on water imported from the mainland. The treaty that allowed the importation of all that water was only set until the end of the lease, and the Chinese very clearly stated that they had no interest in extending it.

Also, earlier when HK expressed some interest in investing into desalinization, the Chinese threatened to immediately cut off the water supply if it seemed like the HK local government would have actually tried to build up enough water resources to make them not dependent on the mainland.

The result of shutting down the taps would have been millions dead within a week. Keeping HK British would have required a massive invasion of China by the UK, just to secure water. I don't see that as very likely.

Hong Kong only began importing water from PRC in 1960. This was as a solution to Hong Kong's water shortages. However, there were other possible solutions – e.g., nuclear powered desalination. Importing water from PRC was the cheapest option, and the UK was more interested in saving money than maximising independence from PRC. If they had prioritised water independence, they would have never begun water imports.

Hong Kong also had its own desalination plant 1975-1981. Why was it shut down – because of pressure from the PRC government? Or because it was significantly more expensive than importing water? I don't know for sure, but my impression is the later was a much bigger factor than the former.

[getting far from the TSMC topic]

If the UK had thought this through, they would have setup real democracy in Hong Kong a generation before the lease ended, instead of doing the colonial "high commissioner" thing. A legitimate Hong Kong government would have survived a lot longer with their people's support.

One could argue in the opposite direction: a real democracy would have been (and still is) an extreme threat to the CCP (Chinese Communist Party) which is an anti-democratic cadre party in the Leninist tradition, and has explicitly stated that it wants to remain one for all eternity. One of the narratives of justification that the CCP uses is that Chinese people neither want nor need democracy.

A democratic HK would squarely falsify this claim.

Indeed, I'd argue that the single most urgent reason (but not the only one) for China 's bullying of Taiwan is precisely this, Taiwan is a thriving democratic and Chinese society.

The PRC kept them from doing that.

Chris Patten tried to introduce democracy in 1992, with less than 5 years to go before the agreed handover, and that angered Beijing yes. And then, when the handover happened, Beijing reversed Patten's reforms.

But if the UK had done the same thing in 1980 or 1970 or 1960 or 1950? I don't think the PRC could have done anything about it.

The UK never really cared about Hong Kong democracy. If they had, they would have implemented democratic reforms decades ago, instead of leaving it until the very last minute.

Not to put too fine a point on it, but the British (colonial historically and more recently) have always seemed to find democracy a bit... inconvenient.

Both for their colonies and for themselves.