David,
I don't think it's a used Wo II commando dagger. I think it's a piece made out of a file

. I tried to make a more detailed pic and added this to the thread. Look at the base of the blade.
The blade is quite 'thick', measuring about 6 mm near the base and tapering towards the point.
Some time ago, I posted a 'Bou Saadi' knife on the forum. Although the scabbard looks similar, I found quite some differences (as Tom pointed out). The knife itself is totally different.
Here's the link :
http://www.vikingsword.com/vb/printthread.php?t=4107