Great Britain includes Northern Ireland. The full title for the UK is The United Kingdom and Northern Ireland
May have got this wrong but I don't think that the Isle of Man is part of the U.K. but is part of Great Britain hence 'Team G.B.' Don't ask for the reasoning behind this but they do have their own legal, tax systems there. Do they still birch yobs there?
In fact it's the opposite way round It's the United Kingdom of Great Britain and Northern Ireland. GB is just England Scotland and Wales. However, the UK competes as the Great Britain Olympic Team (don't ask me why though!)
Isle of Man isnt part of the UK or Great Britain. Its just part of the British Isles (like the Channel Islands)
Isle of Man is not part of the European Union. As Winston Churchill said -- 'the English cannot draw a straight line without smudging it!'