Potatoes - when to harvest?

I have 4 Potato bags each with 2 Charlotte, they have grown very well and have now started to flower...I take the next stage will be the foliage dying down....?
When is the best(right) time to tip the bags out and see my potatoes(hopefully)?

 

Does the foliage have to die down before I can harvest?

 

Maincrop being lifted for winter storage - probably a good idea.

For eating now - lift one and have a look at the crop and decide if they are "read enough" (decent sized tubers have formed) for eating. If all you get are tiddlers then wait a bit longer

Generally if they have finished flowering they are ready but not all varieties flower, and even then not every year, and we start harvesting First Earlies long before they flower - because we are prepared, and have enough land to be able to, sacrifice crop yield for earliness and being able to eat-our-own