https://en.numista.com/catalogue/mint.php?id=31
The current KN page says operation ended in 1962. Wikipedia says the mint was incorporated into Imperial Chemical Industries in 1926 but doesn't say when operation ended.
I found a collectors.com forum post that says operation ended in 1991 but I don't know where that text came from, other than being accredited to “David Vice Numismatic Researcher”.
Backing the 1991 date up, I searched and found Schön says the 1991 issue of N#1599 was produced by KN.
But on the next page Schön says the 2001 issue of N#11523 was also produced by KN.
Does anyone have reliable information on when KN stopped producing coins?11523