The United Kingdom did not aggress and was not aggressed upon. It's that simple.

Area doesn't translate into GDP. Modern day Russia is the world's largest country and largest oil producer, and still manages to have a smaller economy than Italy.

I'd also like to add that the United Kingdom isn't this world's superpower in the same manner that the United States is the real world's superpower. The superpower designation that I used in my NS is based on their having the largest economy at present. They do not have the same unending influence that real world America enjoys.