I've lots of small potatoes left over from last years harvest that are
shooting nicely. What is the wisdom of using them in place of buying seed
potatoes? Is there likely to be any downside to doing this?

I vaguely recall doing this was the cause of the Irish potato famine, since
none of their potatoes were resistant to blight because they never actually
planted "seed" potatoes?
As a point of interest are Scottish seed potatoes actually the result of
growing potatoes from the seeds of potatoes?

Norman Digger.