"very rare prototype enfield ww1 spare mag. Carrier for smle rifle" (?)

[5thBatt]

What I was suggesting is that it may not be WW1 vintage. From the list of Changes regarding the Magazine Lee Metford (actually Rifle, Magazine, Mark I): "One magazine is attached to each rifle, being secured from loss by a chain link; a spare magazine is also issued with each arm". That spare would have to be carried somewhere.

Ridolpho

The Mk1 Metford was originally issued with a spare magazine but they were ordered returned to stores in late 1890.