Potato blight....

It's fine to plant in the soil, but avoid where they were planted last year, if you can find that out. You might get some of last year's crop poking their noses up- those should be dug up and thrown out. Blight spores need living material to survive on, and don't usually like cold so are likely not to have made it through the winter.

There's some more info here: http://www.allotment-garden.org/vegetable/potato/potato-blight.php

Brilliant thanks I have been coming across lots of veg that wasn't harvested and that's gone in the chimnea with the couch grass roots today. I think I'll do a couple of bags just to make sure I've got them all out, they seem rather spread out

Hahahahaha they do seem to breed! Not very pleasant to pick up either even with gloves on