Wallop/Wollop

codswollop

That posting is mostly correct I think. The wallop part isn't though - that was a term for beer lomg before Mr Codd.

Which spelling/

Interesting thought - the part of Belgium near Brussels is called Wallonia and the language Walloon. That area has a long and distinguished history of brewing - is there some link between the idea of Wallop and Walloon?

Merriam-Webster online says:

One entry found for codswallop.

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

As far as I know it was a patent medicine in Britain in the late 1800s/early
1900s. I think it was a kind of cod liver oil or something that purported to
be good for you (and no doubt tasted vile) but actually had no effect
whatsoever. Anyways, as a result Cod's Wallop as it was known colloquially,
became a kind of byword for stuff that was supposed to be good but wasn't,
if you see what I mean. It's all a load of Cod's Wallop!
mejac.palo-alto.ca.us/leica-users/v19/msg06124.html