It's not very clear from the picture, but the billhook like section has a cutting edge. The isn't a hinge.
I discussed it with a countryman yesterday, and he thinks it may have been used for splitting ash branches. I'm going to see him today, and he will have a look at the actual tool. He has also offered me a collection of old tools, so I am interested to see what is in that collection. Maybe I should start an old tools site.
