"Then of course there is the famous Irish song 'Dirty Old Town' :-S
DeG"

Yes, I think from the :-S you ARE winding us up Dave, but Susan-Marie thinks you're great for suggesting it, so what the hell?
WE have also been asked to sing "that Pogues Song"

S-M, it was written by Ewan McColl and is presumed to be Salford, England!

As for "what is an Irish song?" have you seen that set of songbooks called "Songs Sung in the pubs of Ireland"? Plenty of English and Scottish ones amongst the Irish ones!