British nationality law is a set of rules that determine who can become a British citizen. It's like a game with some rules that people have to follow to play. Hong Kong is a place in China that used to be controlled by Britain until 1997.
In the past, Hong Kong was ruled by Britain, which meant that people born there were automatically given British nationality. This means they were allowed to live in the UK and enjoy the same rights and benefits as British citizens.
However, after Britain handed over control of Hong Kong to China in 1997, the rules changed. People born in Hong Kong after that date were not automatically given British nationality, but some of them may still be eligible if their parents or grandparents were British.
Today, if you're born in Hong Kong, you're not automatically a British citizen. You have to go through a process to apply for it, and there are certain requirements that you have to meet. These requirements might include things like having a British parent or grandparent, or living in the UK for a certain period of time.
So, to sum up: British nationality law determines who can become a British citizen, and people born in Hong Kong after 1997 are not automatically British citizens, but they may be eligible to apply for it if they meet certain requirements.