Bob Hobden wrote:
I do hope you find what it is and where it's come from. We saw, two years
running on our old allotment site, a large jet black butterfly with white
dots along it's wind edges, and which flew unlike a normal butterfly but
fast and straight like a bird, but never managed to track the species down
other than it wasn't European.

I'm sure you looked into it - but (I'm papillon crazy) have you looked
at the Peppered moth. It's characteristics is that the black varied
from jet black with white dots on the edges to grey and peppered with
white, hence the name. What was the underwings colour? (I'm hoping one
day to see a white plume moth - I'm keeping some bindweeds in the edges
for it as it feeds and lives. At least it's a reason to give to the
neighbours for keeping the bindweeds ....).