NAPOO
It is a bastardised French like "San fairy ann" is ça
ne fait rien,.
The old WW1 satirical journal, The Wipers Times" (Wipers being a jovial
deformation of the name of the Belgian town Ypres), and quoting a nice
quatrain by Gilbert Frankau, he concludes:
The Wipers texts, both prose and verse, are full of slang still vibrant and
uncontained; a famous example is na poo or narpoo, from the French 'il n'y a
plus', meaning 'there's none left', or more generally, 'no good'. Hence:
The privit to the sergeant said
"I wants my blooming rum."
"Na poo," the sergeant curtly said,
And sucked his jammy thumb.
Another source; The Cassell Dictionary of Slang lists it as:
napoo [1910s-40s] finished, ended.
Frankray