Seed potato harvest

This has been an unusually cool fall for us.  I put a late crop of potatoes in the ground to use as seed potatoes for next year.  What is the latest I can harvest them?

That really depends on your winter climate and your pest pressure. There is no advantage leaving them in the ground after the leaves have gone, but they won't go bad as it were if you do leave them longer. the risk is slugs, voles etc eating them. And of course the ground freezing.

Pretty much my thoughts.  This is my first serious attempt at a late crop for the purpose of replanting in the spring. Of course, everything has gone wrong weather wise.