Yeah, they should have kept ALL of their empire, instead of allowing all the rif raf to migrate to England. Hong Kong was on a 99 year lease. The lease expired and they returned it per the agreement. The (sic) Pomms have a nasty habit of honoring commitments.
I think it was the mainland areas of Kowloon and New Territories that were under lease. Hong Kong island was not. Would have been hard to just have the island.