A Commonwealth-made BAR of unknown origin. I speculate that this is of either Australian or Canadian manufacture judging by the British style open buckles and suspenders. There are no markings except for the "FIX" brand push-the-dot fasteners.
I could not find any online resources referencing this type of belt, so it is most likely a very limited procurement item, issued alongside US-provided BARs.
Circa 1940s/1950s