One of my pet peeves is when people talk about England and the UK or Great Britain as if they were exactly the same thing. Or when English is used as a synonym for British. Both views overlook the existence of Scotland, Wales and Northern Ireland. Although I suppose the confusion is understandable. In the US we stress the role of England during the Colonial period (although after 1707 the Colonies were British). And, in reality, how many countries are made up of four separate nations?
For an explanation of the various parts of the UK, Great Britain the Commonwealth and more, visit this post
The Difference Between the UK, Great Britain, and England Explained from Free Technology for Teachers. Embedded in the post is a YouTube video which details the differences and divisions in just over 5 minutes. It is entertaining and informative, but the narrator speaks super-fast, so you'll need to listen carefully.