The problem really isn't apparent on the photo and I'm concerned because although Stiltons #1-#4 have had a selection of issues, none of them have exhibited this 'sliminess'. The slightest touch seems to rub off the rind and expose the paste beneath (hence the 'bald' patches).
The humidity in the little fridge is nothing like 90%. I try to increase humidity by draping a damp paper towel over the shelf. I think that it's around 70-75% most of the time. The cheese itself is in a plastic box with the lid loosely laid on top. I'll carry on airing, maybe for a little longer each day, and see how things progress.
Many thanks for the cheeses. In celebration of having of having reached a total of six cheeses I've decided that I need an avatar. It's a picture of my home city