Testing prior to installation in the next tunnel, and I'm getting a few images that look like this;
GIMP is saying Unexpected end of JPEG file...
Anecdotal evidence on the internets suggest it's the sd card, so i'll try changing that first.
Using a Samsung Pro 32GB card like this one seemed to mitigate the problem for one night, then the corruptions begin again. We are also losing files - the whole image is black and only about 127kb;
(I wouldn't actually recommend you buy it from Maplin)
I don't know if it really is the SD card.
This seems to have been cured by the last GoPro firmware update. It wasn't the SD card.