I ASSUMED the split had to do with a couple things. Either historical problems with getting ipc like value from india and islands in the pacific to england, or a certain amount of local demand for resources to be spent for the protection of at least their hemisphere.
If the british player can decide where to spend 55 dollars each turn it makes him and the allies stronger. Sea lion is easier to defeat if you can plop 8 tanks in england on UK1. On UK2 they can plop 55 bucks back in india to make up for it.