Eriothrix rufomaculata (Tachinidae)
Quite distinctive in the field with red abdominal side patches, slightly shaded wings and a silvery face with protruding mouth edge. The only species that you could confuse with this is the much rarer Mintho rufiventris but Mintho has a laterally-compressed abdomen and 2 broad black longitudinal stripes on the thorax - contrasting with rufomaculata's cylindrical abdomen and 4 narrow stripes on the thorax.
This is an extremely common fly in mid summer. The hosts are the subterranean larvae of crambid moths but, despite this being one of the commonest parasite flies, this fact was only very recently established.