The No4 Mk.I has a BNP proof mark (nitro), postwar, and a date of 43 on the stock brace, slightly worn or rubbed.
I remember in the early 1970s when I got my first rifles, there were no deactivateds then, firms in the UK were offering smooth-bored military rifles for collectors purposes, so then these weapons were converted to smooth bore, under the condition that the collector has a shotgun license. So in those days you had to send your shotgun cert with your order. There were firms in Birmingham and Wolverhampton,etc., who had stocks of WW1, WW2 and earlier weapons under these conditions. C