The British Isles Demystified
Gill links to Sam, who’s rendered a handy, dandy Venn diagram that clarifies the difference between British Isles, Great Britain, the United Kingdom et al. Sam lives in the British Isles, so she ought to know.
Of course, things get kind of complicated in Northern Ireland. At least half of those folks would disagree with them being the union intersection (math, it ain’t my strength) of Ireland and the UK.
In an offline discussion about which dots are countries, my friend Karl confuses matters:
That depends on how you define “country”! Scotland & Wales - and
sometimes Northern Ireland - have a devolved government with lots of
local responsibility. Scotland & N. Ireland (dunno about Wales) have
their own banknotes and police forces. But the tax is collected
centrally and controlled by the UK government. Everyone in the UK can
vote representatives into the UK parliament. The defense forces are
controlled by the UK department of defense.So if a country is an entity that collects & spends its own taxes, has
a government and an army, then the UK is the country. But if a country
is an entity with a soccer team - a much more valid definition, really
- then Scotland, Wales, England, Northern Ireland and the Rep. of
Ireland are countries.Of course, if you’re a rugby fan, then the countries are Scotland,
Wales, England and Ireland (north & south).
sean 
Cormac