"Christmas in the Trenches" is a parody of "Christmas [Day] in the Workhouse" (or vice versa) (Vice Versa, that's the assistant poet)

Christmas in the workhouse is recited as a poem, usually.

(with heavy london accent, if you can. ) (there I go getting snotty again)

I started to write it in dialect, but I've given up

CHRISTMAS IN THE WORKHOUSE

It were Christmas in the workhouse, the best time of the year.
All them paupers, they were happy, they were full of Christmas cheer.
And, the Master too was happy, as he strode down dismal Halls.
And, he wished them "Merry Christmas", and all them paupers answered, "Balls".
Which made the master angry and he swore by all the Gods,
""YOU'LL GET NO CHRISTMAS PUDDIN' YOU LOUSY LOT OF SODS"
Then up stepped a war scarred veteran who'd stormed the Khyber Pass,
"You can take your Christmas puddin', Mate, and shove it up your .............