Prototype .22 No5 Rifle.

[Warren]

Tend to agree with you on it being an earlier variation.....however, we both could be wrong as it is a Lee Enfield.
Attached is a photo of a pair of No.5 .22 rifles and the stock on one is almost a dead ringer for our mystery rifle. The other has a military pattern butt however with a checkered grip.
I'll take a couple of shots of the actions later today or tomorrow, but just no time right now.
I just dropped in to see what was new.
Attachment 80506