I have a set of those plastic grip scales myself. I have yet to handle a 'Correct' Bayonet with them affixed!

I THINK this particular specimen, MIGHT be a foreign contract version? The OFFICIAL Sterling COMMERCIAL No.5 Bayonet
Had Metal grips as we all know. AND, the Etched word 'STERLING' in a rectangular box on the Blade.

I would be interested to know for sure. Which Country Made/ obtained the plastic gripped variants?....