Common Blue

Okay, it's a bit of a rubbish photo, especially compared to those on Bob's Butterfly Blog, but I am doing this late (again) and it's to hand and I know what it is. It is a Common Blue, Polyommatus icarus, and what's more, it's a male: the females are brown (unless you live in Ireland or north-west Scotland where you might come across the blue marsicolore form). It was in my garden the other day whilst I was slaving away trimming some hot beech hedges. 
The explanation for why their wings are blue is fascinating and complex, but too elaborate for me to divulge at this time of the night. I refer you to the excellent Messrs Thomas and Lewington.