Just had my delivery of seed potatoes 16th Jan 2 months before planting, I contacted Thompson and Morgan's to be told tough nothing that they can do and no advice on how to store them. They are in a cupboard in complete darkness is this the best way to store them? p.s. I won't be ordering from Thompson's again!!!
I would put the potatoes out as though you are going to chit them (in my case, I put them eyes-uppermost, in egg boxes) but keep them as cool as you can without them actually freezing. That way, if they do keep growing, they'll develop properly without getting drawn or distorted, or the shoots broken off when it comes to moving them / planting them out / disentangling them from their net bags.
Regarding Marshalls, it's no surprise they're so expensive when they're always reimbursing folk. They seem to be yet another company that's lost its way, probably as a result of a buy-out. It's hard to know if the chicken or the egg came first, though. I can no longer recommend them, which is a shame.
I just realised that I asked the original question in this thread in 2008! And I certainly still keep mine that way now, that is, in the cold but frostfree garage in their original packing but opened up for some air. When I can see the first shoots on the move (which probably won't be for another two months or so), I put them out in egg boxes to chit in the unheated greenhouse but cover them up when it's really cold.
Our potatoes are not planted out until April at the earliest, the earlies in pots and bags in the greenhouse, the bulk on the allotment in May.