The symptoms were:
Prior to the jam the film advance was slightly stiffer than usual.
Once jammed, the film advance crank would turn as freely as when there is no film in the camera.
The shutter would never prime nor the film transport lock - you could keep turning the crank as the film would never advance.
Brass swarf in the film chamber(!)
Once the film was removed, holding the film take up spool whilst advancing the film you could feel very little torque being transferred to the spool.
Film backs for this camera are still pretty expensive, so I was keen to try to fix this one rather than just buying a new one. It turned out to be a pretty straight forward fix and didn't require any replacement parts or special tools.
Step 1: Disassembly
A small Phillips screwdriver,
A small to medium flat blade screwdriver,
Two pairs of needle nose pliers or small general pliers and
Remove the film back from the camera and then remove the film insert (see photo) from the back, as this is the only part we will be working on.