This year my potatoes were looking good for a bumper crop. However when I dug the first earlies (Lady Chrystal) I noticed quite a lot of rotten tubers. I dug a maincrop (Pentland Hawk) and it was even worse - about 70% rotten. The tubers have black/blue blotches on the outside and sometimes white spots on. On cutting the tuber the rot is clearly coming in from the outside as the centre looks OK The rot is in the shape of brown rings. The plant tops have shown absolutely no signs of blight. Generally the tubers nearer the surface seem to have survived better.
We had (in Birmingham) lots and lots of rain in June then very dry ever conditions since (desperate for rain now!). I have clay soil and my plot is on a slope.
Any ideas what's happening?