This one was converted from a BSA Sht LE MkIII (unsure if III* from pics) prior to 1926. This .22 trainer pattern was to be the last for the No1 rifles, and became the Rifle No2 MkIV from 1926 onwards...and were still being converted in Australiaicon to this pattern into the 1950's.
Would like to see the FTR markings, I would have to do some checking, not sure the trainers were FTR'd... maybe someone else will know for sure.