Hi Clivvy
I have one exactly the same, had it for so long I've forgot where I bought it but probably at an ex army store somewhere in the UK. I keep it under the back seat of my T2 'just in case'. The blade can be locked in the position yours is or at right angles to the handle, to use it as a 'pick' for 'digging in' or it can be folded flat against the handle for compact storage. That is of course if the castellated alloy nut just before the blade, can be screwed back or forward to lock the blade in the required position. It looks like yours, after years of being buried, might need soaking in an oil bah for a while before you can move it. As for whatever tales it might tell - who knows?
Rgds CL