Thank you for all of the responses. The FE's plate is non-dimpled. I have taken the plate off of the back and had a look and run a finger across, but there doesn't seem to be much. There was a tiny bit of dried stuff that I have removed, but that doesn't explain the vast majority of the scratches. The scratches are continuous, one side only and parallel to the film transport.
I don't see any obvious particles, but I'm well aware that even something tiny could cause this. The scratches are across the frame - not on a specific height.
The HP5+ was straight from Ilford, as was the Gold 200 roll that I cannibalised for it. The HP5+ was loaded straight from the film canister into the camera.