Just managed to get the camera going again - amazing what recharged batteries will do these days -

The discolouration across the top of the black strip is the grotty part of it whilst the lighter colour between it & the black strip is where I managed to cut the thicker parts off with the pocket knife.
Looking at it as I took the pic, I think I'll attack it again with the flat blade of the knife... reckon I can get a bit more off.