Newbie Potato Grumble...

Indeed it is Mum. 

It's not such a big problem here as the fungal diseases of potatoes but in warm climates like Spain it's much more of a problem.

http://www.growingpotatos.org/blackleg-and-soft-rot/

http://www.potato.org.uk/department/knowledge_transfer/pests_and_diseases/ref.html?item=11

Sorry for the super-late response to this.

@DD: the potatoes were a gift from our neighbour. She says she's using the same batch for hers and they're fine.

Quick update, the remaining 20% were also ruined, so they've been taken out. A very sad day. Anyway, we're preparing the ground for something that we can put in this late in the season.

The neighbours think we're mad. Even though none of them saw the infection they all claim to know best: it was mildew and we're stupid for removing them. We should've carried on using fungicide on a bacterial problem.