Surplus firearms whether they be No4 rifles, handguns or shotguns were sold off by the Ministry of Supply disposals.
As there was such a huge variety of shotguns by different makers that were acquired during WW2, it made sense to rationalize was was kept, so that armorers could work on a more limited range.
Interestingly, the RAF still needed shotguns in the 1950's as this is when the 1,000 order was placed by the Air Ministry with BSA for their DB boxlock known as the Regent. These all had a W prefix to the serial number, 28" barrels and semi pistol grip stock. Country to popular belief they are not wartime issue guns.
I bet Webley & Scott were miffed that they did not get the order for the 1,000 shotguns for the Air Ministry.
Regards
Alan
