Mystery Fly

This fly was resting on a grape leaf in the light rain.  It is a new one to me.  It is about 20mm long, and the most noticeable feature is the dark shading on the ends of the wings.  I wonder if it is a robber fly of some sort.  Although different from the common robber fly there are a few similarities.  Or it could be a soldier fly.  The four spikes on the scatellum above the waist are rather impressive. More obvious in large.

Edit: Tessa has identified it- it's a garden soldier fly, Exaireta spinigera.