Tbh I have to agree with Angelscotboi here, With Elizabeth and Longbowmen this is a English Civ, similarily, you wouldn't call the Italian Civ "Roman" if you had Silvio Berlusconi as its leader, obviously though Rome is and always will be the better choice for a Civilisation. England will also be the better choice over Britain, it's existence is longer than that of Great Britain or The United Kingdom, It also allows for Scottish/Irish/Welsh Civ's to be considered, Scottish would probably be the better of the three, viva la William Wallace.
Truely though, the Civ "England" refers to the English and not the British Empire. Thus it is named correctly. However, Britain could be used just as easily as England for the Civ.
However you would be referring to more than simply "Wales Scotland and England" you would be reffering to periods such as Roman Britain as well as Great Britain. Where as with England you know what you get.
P.s "America" is not an accepted short for "The united states of america" (even the proper title is incorrect, it should be "selected united states of America". America or as it was also known "The America's" consist of South America & North America. Their are many countries in South America, such as Brazil and Mexico and many more, where as North America only consists of (correct me if i'm wrong) the USA and Canada. But Canada is in America, so are all the countires of South America, so no America is not known or a correct short hand for The USA. Anyone who uses it as such is just as ignorant as people who think thier is no difference between the United Kingdom, Britain and England. The only reason America is used as a "ignorant shorthand" is because its easier than saying "The United States of" each time you say it, just as we call the United Kingdom the UK for short. That doesn't however make the "shorthand saying of America" in any way correct. Perhaps you should have chosen a better name for your country than that of the continent. So yes the USA is also known and refered to a lot as simply America, but that doesn't make it any more correct, it just makes a lot of people more ignorant.