This explanation may also be a load of codswallop...
>FishOnABike, you gonna take this sitting down?

Well, Auntie, sitting down doesn't mean motionless if you're on a bike ...

Merriam-Webster it say:

Main Entry: cods·wal·lop
Pronunciation: 'kodz-"wä-l&p, 'kädz-
Function: noun
Etymology: origin unknown
Date: 1963
British : NONSENSE

Interesting, but not very informative.

Nice as it would be to relate the first use of the term to around my time of birth, I suspect it may have some relation to the old "God" = "cod" (Shakespearian) thing.

Although wasn't there a verb to cod meaning to wind up, take for a ride or whatever? That would be apt.

Calling The Supreme Universal Word Master!