It is a very slim fly, mostly less than 2mm across and about 10mm or so long with a wasp-like reduced waist. At first glance you would think it was a wasp, but comparitively docile and not easily scared off. The first one climbed onto my finger and I had to put it back on the leaves!
I was lucky to find both male and female within a few days in my garden. I have named them Fly 1 and Fly 2 for convenience, as I am not absolutely certain which is which, but my guess is that Fly 1 is the male as the eyes look to be closer together. I would also expect the club tail of Fly 2 to be that of the female, but I may be wrong!
There is very little information on this fly, I found an article stating that the larvae are found under the bark of fallen trees.