It's actually a good song, though the Wolfe Tones' version is pretty awful - they're a shouty kind of a band.

It starts:

When boyhood's fire was in my blood

I dreamt of ancient free men

Of Greece and Rome who bravely stood

Three hundred men and three men...

(a reference to (respectively) the Spartans at Thermopylae and Horatio on the Tiber bridge defending Rome from the forces of Clusium).

By the way, Dave the Gnome, "British people abroad, including Irish" is inaccurate - it's a bit like saying "Canadians abroad, including New Yorkers".