Polymorphic Fly (Nowickia ferox)

This female tachinid fly was one of two bee mimic flies in my garden this morning. I can't immediately identify them but I'm sure someone can help. This one posed obligingly on one of our osteospermums

 

The image should enlarge nicely if it helps with the i/d.

 

Thanks to Judy and Andrea for help with the i/d.

Done