mystral: England is self-explanatory, Great Britain is just the biggest island (England + Scotland + Wales), the UK is the actual country (the one that has a seat in the UN for instance) and includes Northern Ireland and possibly some other small isles like Jersey.
cheesetruncheon: England is the Country Of England, Great Britain is Comprised of three separate countries, England, Scotland and Wales that Create a Sovereign State, the United kingdom adds Northern Ireland.
The British Isles is Great Britain, Ireland and the outlying Islands.
but yeah Scotland, Wales and Northern Island all have their own governments, and the people tend to get pissed when you don't acknowledge them as a country.
Well, sorry if I offended anyone, but the fact is that from a foreigner's point of view, a country is only one officially if it's recognized by other countries, and a seat in the UN is part of that.
AFAIK, while Scotland, Northern Ireland and Wales have some autonomy, they are NOT independent countries, and their "government" has limited power. They have no say in defence or foreign policy, and therefore can hardly expect to be acknowledged as actual countries.