An Eriothrix rufomaculata (Diptera: Tachinidae). Identified using the key of Belshaw (1993).
This specimen is unusual in having a large gap in its medial vein near the tip of the wing. This gap was present on both wings and so was probably a developmental anomaly rather than a result of any damage to the fly while it was an adult.
Specimen taken in Whiteknights Park, Reading, UK, on 2014-08-03.