Dicho,

"Derby Kell" is a shortening of "Derby Kelly" - Belly (and, If I remember correctly, the "Derby" of "Derby & Joan") and appears in another (I think) Champion song "Boiled Beef and Carrots"
"....That's the stuff for your Derby Kell,
Makes you fat and keeps you well..."
"Corporation" for a large stomach used to be fairly common in London too. An interesting version was also (the maritime influenced) "tumblehome", not common, but certainly used (the "tumblehome" was the bulged shape of a wooden ship in cross section, wider in the beam than at deck level).

Walrus