There are some key elements that are not being address in your argument. The fact is that Britain (and France) were greatly weakened during the Great War and were reluctant to enter WWII because of that. Afterall, both countries lost millions of men between the ages of 18 and 42 and could not afford to support another war. They wanted to avoid another WW1 at all costs. The other point is that in order to sustain its war effort during WWI many American businesses, merchants and banks in particular, loan a great deal of money to Britain so that they could obtain arms and materiel tosustain the war effort. This put Britain in great debt to the U.S. that they were never able, or didnt want to repay. For that reason the Treaty of Versailles was written so that the Germans would except total fault in WWI and would be forced to accept the responsibility of making reparations to Britain and France in the form of cash and raw materials (Iron, coal, etc). Because Germany after the rise of Hitler rendered the Treaty of Versailles null and void, Britain and France never got all the reparations that was due and therefore never repaid their debt to the U.S. This was one of the causes of the Great Depression in America. The fact is that once France was defeated in 1940, Britain was left to fight Germany on its own. It is very unlikely that they would have had the resources to fight Germany, hold off Japan and protect its interests in India and southeast Asia. Remember that once the French folded, they were force to cede French Indo-China to Japan putting the Japanese at the back door of British colonies in southeast Asia. Japan's goal was to get to Indonesia to retrieve the oil there which they desperately needed to support their war effort because of the U.S. oil embargo. So, if your saying they would have been able to accomplish this all on their lonesome, that would have made them an incredible fighting force indeed.