I
think this is a 30-round magazine:
These are Norwegian Commandos,
probably on Walcheren in late 1944, who for some reason are guarding a group of German prisoners with shovels, so I suppose this is after the fighting.
However, I couldn’t find any other photos of Commandos with 30-round magazines (except one of this same man, taken from a different direction), when I would kind of expect Commandos to want larger magazines if those were to be had. For all we know, of course, if this fellow does have a 30-round one, maybe he got it from an American somehow …