We used to get it ,in Devon,for breakfast in the navy, at RN Barracks, Devonport, and HMS Raleigh ( Torpoint ).------Although it wasn't black, it was white, and it was called Hog's Puddin',not Black Pudding, but otherwise very similar stuff.--quite tasty ,actually. I expect Cyril Tawney would have known some obscure naval slang for it, as in chicken-on-a-raft ( egg on toast,), train smash ( streaky bacon and tinned tomatos ) Spithead pheasant ( kipper ) , or babies' heads ( individual steak & kidney puddings ), not forgetting hammyeggycheesey, ( or UITSMIJTER in Holland!! ), and Harry Thickers.