Pontia daplidice - Bath White

Pontia-daplidice-bath-white | PTKbutterflies
Pontia-daplidice-bath-white | PTKbutterflies
Pontia-daplidice-bath-white | PTKbutterflies

This and the last species are morphologically very difficult to separate, so identity relies on location alone, these being sufficiently far west to be reliable. 

They are beautiful and delicate, and often not easily approached for butterfly photographs.