Personally I would chuck it. I'm not keen on using seed from my own plants as we tend to take potatoes for granted. If a disease like blight gets in to them then the results are a disaster all round. Seed potatoes are not all that costly and will ensure you are not harbouring the beginnings of an unseen and unwanted freeby. It is less likely to happen if you use fresh seed and rotate the places where you plant each of your crops.

Hate to disagree, but we often allow these wildings (volunteers they are often called) to grow on. In fact we often get a better crop from them than the planted ones. If you did not have Blight last year then these tubers should be safe. Moving them elsewhere though might be a problem, never tried it so no idea if the root disturbance at that stage would have any effect on the growth. Suck it and see is my advice.

give it a try you have nothing realy to lose .

Thanks Guys,
I've put two of them in separate, large pots and will see how they go.

good luck .

Last month I dug up several self set potatoes that were beginning to shoot and transplanted them into tubs and put them in the greenhouse. I do this every year and am always delighted with the results, generally a good crop and nice and early too. Last year I re set some self sets into the vegetable garden and had once again a good crop from them.