I'm not that familiar with the Hong Kong treaty. From what I've read, Hong Kong citizens (British National Overseas) during the British rule were treated as subjects, but were not accorded full British rights. Meaning that they don't have Right of Abode in the UK. But try, you might have a chance with that if you are otherwise than by descent. I am not knowledgeable enough when it comes to the Hong Kong-British relations.
Sadly, no. That just gets you the useless bit of paper called a BNO passport which lets you travel round ASEAN but nowhere else. I'm an ex resident of HK myself. I have lots of friends with that bit of paper. Wish I could be more positive, but the only way that I can see for you to pass on British nationality to your son is to move to the UK with your family for five years... not an inviting prospect, I know.
I'm afraid you're right, Methersgate. I actually did a bit of digging around online today on the whole HK issue. My poor head can only take on so much technical information in one sitting. But, yes, it does look like the only way to pass on citizenship would be to move to the UK at some point. Would I be right in thinking that he'd be considered British otherwise than by descent if citizenship is acquired that way? If so, then it can't be that bad, can it?
Yes, he would become British both ways - "as British as its possible to get!" Which would mean that his children could be born outside the UK and retain their British citizenship "by descent"...
Now the fun starts... you have Right of Abode.. but your son and your fiance do not... so you have the right to settle here but you will need to jump through all the hoops (financial requirements etc) involved in having your family join you here, if you want to take that approach.
