Agreed, but here's some more detailed evidence, from Ian Hogg:
232 Fuze, Percussion, No 232
Design DD/L/J13250. This was the original titIe for the Fuze No 231 without the delay unit.
It was cancelled, and after July 1941 the design became the Fuze No 231ND.
Announced in IOO's Ammunition Bulletin for May 1941, Item 252, which referred to the
232 Mk 1.
Filled Lots Nos 1 to 26 were accepted for service. Lots 5 and 6 were rejected at proof, and no
more were filled. OB Proc 32537 of 9/11/1945 refers. It is doubtful if any Mk 1M were ever
made, the design probably being sealed for record only.
Mk 1 §B7985 of 25/2/1943 "Belated announcement" of introduction
Mk 1M §C969 of 25/10/1943 Shutter fitted with detent stop.
All Marks Obsolete by §C3176 of 3/9/1947
Your fuse is a very special example.
Depotman