Any erosion of Hong Kong's economic independence could not only threaten its desirability as an international financial center but hurt China as well, the last governor of the former British colony said in an interview, adding it was inevitable that the authorities would have to give residents greater sway over how the territory is run.

Speaking to The Wall Street Journal during a trip to Singapore, Chris Patten – who governed Hong Kong from 1992 to 1997 – said the core challenge for Hong Kong had always been to combine its...