Only way to find out is to go looking under the plant. The foliage on our earlies has begun to die down, so to us that is a sign that they are ready for digging.

I've started harvesting mine now. Some of mine are doing this so just assumed it was normal behaviour.

I steam them but the skins still split. How do I get round this, do I need to leave them to 'dry off' in a cool dark place or was it down to variety.

Just to let you know that the one with dead leaves has now been 'harvested' to reveal that the tubers must have died at some point. I got six small potatoes, lovely of course and which I can use in a potato salad. The other three are very green and will hopefully harvest as usual. I wonder why these things happen.