[khuey]

It's worth noting that the Qing Dynasty ceded Hong Kong Island and Kowloon to the UK in perpetuity. The lease was for the the New Territories, without which it was generally accepted the city would not be viable. Hong Kong was (and still is) dependent on the Chinese mainland for imports of natural resources such as fresh water, so if the Chinese decided to play hardball the British had few options. And that's not even considering the possibility of China deciding to retake Hong Kong by force.