Thanks to Paul L.Th. Beuk for correcting my misidentification, he says The fly pictured on the page below is not Opomyza florum. It is an Heleomyzid (easy to recognise by the regular spines along the naterior wing margin) and I think it is Suillia variegata.
This picture is of Suillia variegata captured in the Sheffield area of
South Yorkshire UK