Fly on knapweed 28Jul15

Fly on knapweed 28Jul15

Observation - Fly on knapweed 28Jul15 - UK and Ireland. Description: Did not realise there was a fly in this photo - image cropped to exclude Large White butterfly nectaring on the flower (knapweed) so image small and not in focus. Is there enough detail to identify fly?

Did not realise there was a fly in this photo - image cropped to exclude Large White butterfly nectaring on the flower (knapweed) so image small and not in focus. Is there enough detail to identify fly?