Potatoes left in the ground over winter can attract potato cyst eelworm and / or can act as a place for late blight to overwinter. I would dig them up and dispose of them in the rubbish. Don't compost them.

How odd, we often dine on 'volunteer' potatoes. It is very difficult to remove all of them when you clear the plot. If you find they have pests in them then dispose of them, otherwise they are just as good to eat as any others.