I normally wait till may and plant the tubers in the greenhouse soil direct. But this year I wanted to start early, So I brought some tubers and left them in a plastic bag to sprout, it took about a week for the roots to appear on one of them. I've never done this way before it was just an experiment. But know I have these roots appear shall I leave them to get bigger or shall I just put it in the compost container straight away.
I've potted some up and kept them in the house before and they seem to spring into life quite quickly. But the last few years I have over wintered them in the greenhouse and they happily re-sprout once the temperatures warmed, though we don't get as cold winters as some areas. I'd pot the one that has started into growth and grow on inside, should make nice plants by planting out time.