I just picked up a book entitled My Pious friends and Drunken Companions and More Pious Friends and Drunken Companions, songs and ballads of convivialty, collected by Frank Shay. (Dover Book of Humor, re issued in 1961, originally two books were issued in 1927 and 1928) Shay doesn't credit Percy, but he does have more verses. Here they are.

We reached the mountains safely tho' all stiff and sore with cramp
Each took a neat of whiskey straight to disipate the damp.
And when their pipes were loaded up O'Slattery up and said
Today's immortal fight will be remembered by the dead.

I never wil forget said he while this brave heart shall beat
The eager way ye followed when I headed the retreat.
Ye've heard the soldier's maxim when desisting from the fight
Best be a coward for five minutes than a dead man all your life.

So there in the mountains rest the squadrons and platoons
The four and twenty fighting men and a couple of stout gossoons
They march no more so martially to patriotic tunes
But all the same they sing the fame of O'Slattery's light dragoons.
^^

(line breaks added by a Joe clone)