Withering Potatoes!

Good Evening,  the leaves on my potato plants are quite brown and shrivelled, despite (or because of?) the copious rain in Hampshire recently.  However, when I am lifting the spuds they are perfectly fine and edible with no signs of damage.  They are Maris Piper, planted 5th May.  Any ideas what could be happening, first time growing them?  Thanks all. 

Oh OK, thanks for that quick response.  As a Newbie I learnt something EVERY day...