Turn Wales into New Hong Kong.
All Wales have going for it is sheep, but the quality is a bit suspect with all the sheep-fuckers also living there. What would China even do with such a pet colony? Trade sheep to the Irish with?
If China was minded to just fuck with the British, it could just take Northern Ireland off them and give it back to the Irish, who I’m sure would welcome a PLAN naval base there with open arms to keep the British out.
Similar deals could be worked out with the Falklands and Gibraltar. Indeed, China could make a lot of great deals and significantly improve relations with a lot of countries by simply seizing and returning disputed lands to various countries around the world.
But the most valuable British remaining overseas territory are probably the British Antarctic Territory. But this is all getting a bit wildly off topic.