Posted: 13/01/2013 at 01:27
Hi Daisytwo, There is a pest called potato eelworm, but the worms are minute and need a magnifying glass to see, so it probably isn't that. I suspect the holes are being caused by keeled slugs and the worms are a secondary infection. Neither of these pests are easy to eradicate, unfortunately. Crop rotation on a 4-year cycle is usually recommended, but your best bet may be doing that and growing slug and eelworm resistant varieties for a few years. This factsheet may help:
Digging up and storing the potatoes as soon as the haulms die back will help, too.