Locust Blowfly
Stomorhina lunata Fly, The real size is 5.81 mm, magnification is 1.4, from Hutchinson's bank
From Steve Falk
A very distinctive, House Fly-sized species with a strongly protruding lower face and striped thorax. Males have large orange patches on the sides of tergites 3 and 4 (=apparent tergites 2 and 3) but females only have grey dust patches here. The sexual dimorphism is similar to that of the Face Fly (Musca autumnalis) and it can sometimes be mistaken for that species or a hoverfly.

S. lunata is a highly mobile and migratory species that is being found increasingly frequently in Britain, though records extend to Sutherland

The larvae are known to develop as predators of locust egg pods abroad but are now thought to use grasshopper egg pods in Britain though it is unclear whether it forms permanent populations here. Adults visit the flowers of umbellifers, composites, mints etc.

The biology is summarised by Greathead (2009)
onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1962.tb01...