Polyommatus icarus - Common Blue
This is the most common and widespread Blue butterfly in Europe. It's violet blue is beautiful when fresh and it can make for a very beautiful butterfly photo.
The females carry a variable amount of blue as shown here.
In 2018 I found the Arctic subspecies to be very different, without the forewing cell spot, and generally much less well marked.
The butterfly images below are from high in the Arctic circle, notably and consistently different...