I used to know this (actually I arranged it from a tape for a charity performance), and if I rack my brains it'll maybe come back. The joke lay in the choruses, for as the example shows, there's a pun--which changes with each verse. One stanza ends "So doff your hat, I pray"--and the chorus repeats "Sod off, sod off" [vulgar British], the point being stressed by ending it "get lost" etc. If there are any other transposed Brits out there, maybe they'll recall it.