Mike Lyle wrote:
Definitely don't wash them: as you suggest, it will impair keeping.
Even brushing the soil off too vigorously can damage the skin. Exclude
the slightest trace of light, and store in a dry and cool but
frost-free place with some ventilation. Cardboard boxes inside
cardboard boxes and then covered with more cardboard or old carpet are
what I've always used. If you've got an awful lot of potatoes and a lot
of space, search potato clamp and you'll probably find instructions
for old-style outdoor storage.

I'm experimenting - I've lifted many when the soil was really wet and
took double the weight of potatoes in mud around them. I laid them on
the table to dry and then I've put them in a wicker sack still with the
dry mud around (quite a thin layer on them) and they've been kept there
for ages. None have sprouted. I supose the mud keeps the light from the
spuds. I'll see if I can keep them like this till xmas.