Need help identifying this Sten

[tiriaq]

In addition to the trigger box missing its ears, the bottom of the magazine housing collar has markings "ES1(?) 2016, caliber mark, and proof marks. Country of proof? Who is ES1?
I am pretty sure that parts of an original were used along with a new main tube to assemble a gun. If this is the case, I can't see it having much value to a collector.