Well, the Morris side I play mandolin for, Bishop Gundulf, dance to this (no, don't ask me why a Morris side might want to dance to an Irish tune) and the dratted thing has been driving me mad for over a year, so I finally sat down with a download of the tune and here are the chords (as I hear them) - in G, just to upset the purists who say that in Irish sessions it is ALWAYS played in A and only an Englishman would play it in any other key...

I (G) am a little beggarman, a begging I have (C) been
For (G) three score years in this (F) little isle of green
I'm (G) known along the Liffey from the Basin to the (C) Zoo
And (G) everybody calls me by the name of (C) John(D)ny (G) Dhu

Of (F) all the trades a going, sure the begging is the best
For (G) when a man is tired he can (D) sit him down and rest
He can (G) beg for his dinner, he has nothing else to (C) do
But to (G) slip around the corner with his (C)old r(D)iga(G)doo