Thank you Wootang, found it now. Diggory reads the mark as K 176 although it looks to me as more like K L36.
I am familiar with certificates of unprovability, issued in the past but I believe now fallen out of favour, and I have seen certificates of proof when a collector’s item has been proved with “minimum marks”.
I have not seen British Proof Certificates otherwise but I am sure Diggory must be right given his wealth of experience.
From the absence of a date stamp the gun he shows again appears to date between 1943 and 1949, but whilst 948 fitted the intervening years 176 or 76 clearly does not.
So not a date stamp then.
