Sacha wrote:
I'll print that photo off and show it to the staff that saw the mystery one.
Blue and really huge was repeated again today! But the photo of that says
'extinct' - which would of course make it lovely if it was that one!

Maculinea arion: Extinct in the 50s, loss of habitat and intense
farming was the cause. It has since been re-established successfully at
five sites in south west England using Swedish stock ... Size 43mm.