Thank you for the reply
In the photos I've uploaded, I've highlighted the arm that has stopped moving when I turn the crank, the handle itself, and the bobbin shuttle. When I turn the machine over to look at the mechanism underneath, nothing moves when I turn the crank handle either. The handle is not seized - it turns smoothly, doesn't wobble and still turns the bobbin winder when it's engaged. The bobbin shuttle arm has stopped moving when the handle is turned too. The feeder dogs appear to be fine and not choked with thread or fabric. Everything was working perfectly until this afternoon and I can't think of any sound I heard or weird movement the machine made before this started to happen
This is my first vintage hand crank machine and despite it looking so simple, it has me stumped!