An orange fly with unusually long aristae, probably a male Eccoptomera sp, possibly Eccoptomera longiseta (Diptera: Heleomyzidae), but there is at least one other member of that genus with long aristae.
A close-up view of the side of the head:
The side of the thorax:
And a dorsal view of the thorax:
Specimen taken in Dinton Pastures, Winnersh, near Reading, UK, on 2014-10-11.