I don't believe that they built many chests - possibly this was for the tool room guns??
I note that the designation is "C.A.L. 9mm Carbine - Long Branch", which leads me to believe that this may well have (originally) had nothing to do with C1 `Sterling`SMG.
A friend has/had a very early C1 SMG "new in box" and it is in a cardboard box...