I guess its easiest to think of as:
England Scotland N.Ireland and Wales are all
countries
UK is the
nation to which they belong.
Neil and I are both British Citizens and herald from the UK, but we are not fellow countrymen, as he's a jock and I am just another piece of English scum
BTW ... in the Olympics we/they enter as:
Great Britain and Northern Ireland ... and not as the UK ... this is because it was decided a long time ago that it would be this way and has remained so since, but also another little known fact is that Great Britain on its own is just the mainland regions of England, Scotland and Wales - it does not include the territories of Northern Ireland.
To clarify something else, I believe I am correct in saying that
The British Isles is the whole group of islands over that way including Northern Ireland and Eire (which is more like saying Scandinavia, Iberian Peninsula or Benelux).
Its all very historical and complex, but this is how things are, and I guess it depends on the rules or entry requirements or personal taste as to what you call yourself or whether we are from the UK, an Englishman, Welsh, Cornish or a simple Lancastrian like myself
(EDIT: Lancashire is a county not a count
ry, kind of a region ... you have something like this in Spain:
we have something like this too (sorry no NI but you get the idea):