hi i have just dug mine up from two seperate lots.the first lot the leaves were dying but they didnt flower,the second lot has just come into flower,both lots of potatoes were very nice,i have been told not to pick them untill the flowers die off but have been happy with both results,you can pull one of the stems up and test for yourself ,if they look too small leave for another week or so.the pictures of mine i put on my home page have a look they were taking off my crop with no flowers.good luck

Once the top foliage has died back, with earlies, the tubers won't get any bigger, so dig them then.
The key thing if you want to store them is to leave the dug spuds on the surface of the soil for 24 hours to dry out in the sun and harden the skins.
Not longer than that though or they will start to turn green.

Remember though that the early potatoes wont keep once dug. Better to leave in the ground and lift as needed. Main crop is a different matter.