That was also the subject of a staistical study done many years ago pre Dunblane. Based on the number of souvenir pistols from two world wars plus a fair number of smaller conflicts handed in at amnesties or just handed over police station counters at any time by relatives clearing out their parents' or other deceased relatives' houses, and given that by no means all would be declared, a figure of getting on for around two million such weapons was estimated to be illegally held in the UK.That seems more likely, also what about deaths, people die of natural causes and stuff gets forgotten about.
With x scores of thousands B&Es per annum, a small percentage, but still a fair number of these handguns would likely be discovered and stolen by professional criminals each year and their loss was hardly likely to be reported!
In my railway industry days, a senior operations manager I knew well started on BR at the tail end of the station master era and his first managerial job was a bunch of small stations on the Manningtree to Harwich branch line. This was an emergency posting without handover as the previous incumbent had died suddenly of a heart attack. My friend's first job was the usual one - clearing out 40 years worth of out of date paperwork, wagon sheet and sack returns and suchlike, but one drawer on the large Victorian desk in his main station office was locked and there was no key that fitted it. On forcing it, the reason became clear - a mint P'08 in a German Army WW1 leather holster with two magazines, both loaded. I asked what he did with it - some village pond after dark!