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