Mortice chisel?
This could on the right lines. I've looked at some images on ebay, and there are mortice lock chisels that aren't straight, implying some rotary action is used. They almost all had wooden handles, though, and there is no sign that the things I have had handles.
The Dell no longer has its cutting edge, either, but it only cost £70. And the 20 pence coin cost me £0.2.