Just to clarify:
United Kingdom comprises England, Scotland, Wales, Northern Ireland, The Isle of Man and The Channel Islands
Great Britain comprises England, Scotland and Wales
British Isles comprises of Great Britain, Ireland and all adjacent islands in the North Atlantic
England comprises of well England!!!
I think I've covered all of them!! That doesn't mean that Scotland, England, Wales and Northern Ireland aren't countries in their own right, they have sort of state like independence....that's the best comparison I can give. Lesson over!! (I'm English and living in USA, I get asked about this all the time, so I thought I had better know myself!)