What is this small black flying insect?
No interactions present.
They can and sometimes do bite but have no stings. There are Trout hooks that mimic this fly.
It is probably this species, the common St. Mark's Fly. The only other possibility is Bibio hortulanus, as it is an all black Bibio with the correct wing venation for these two species.
My Flickr photos...
Lat/Lng: 51.2919, 0.1814
OS grid ref: TQ521570