Firstly this is totally unrealistic as Tucker said, its near impossible to rule over that sort of empire effectively and keep hold of it. The British Empire couldn't even hold on to Ireland and that was right next door, what hope did it have of keeping hold of the US?
However if you do ignore the difficulties of governing a state from the other side of the globe you would have an empire on which the sun really never would set. The US, Australia, India, half of Africa, and who knows maybe even the majority of Europe.
The problem you'd have in these times however would be that whilst England would be in control of these areas how do you define the control? There is always going to be opposition to any form of government and this opposition is usually unifed when the governement is from the outside of your homeland. Look at how India dealt with the Empire before it won its freedom, everyone, muslim, hindu or whatever other denomination was pretty united in their aim of getting rid of the colonials. This would simply be going on in every other state that the Empire consisted of, other than Scotland Wales etc. but they are to close to be a problem. Then you've got to worry about the other major powers that are present in todays world, China and to a certain extent Russia (the US doesn't count as its part of the "Empire") Both Russia and China would of course be very interested in destablizing the British Empire and getting some of the pie for themselves. It may end up being another Cold War, with three sides. You'd also have to take into account the size of their potential empires, as if the UK was able to keep an empire surely they would be capable too.
This also begs the question of the other major colonial powers of the colonial era, France, Spain, Germany, what happens to their empires? Before the colonies were almost all granted freedom the international politics surrounding these countries were very tense, hence the almost constant wars throughout the latter half of the 19th Century up to the end of the 2nd World War.
So England could be at war with countless other countries, but assuming that it still held all of its colonies it would still be the biggest power in the world and as such should still be able to deal with all the threats. It would be todays America, but with more land. This also means more to defend so maybe it would be even more vulnurable than the US is now. Of course whose to say that the Empire wouldn't have simply carried on rolling and taken everything it wanted. I just can't see people such as the Chinese submitting to British rule quite as easily as the African colonies did.
Nice subject... soooo large!!!
