I've had 2 replies to my query. The first suggested a male of the Coccidae family (Scaly-bugs), which is very doubtful. The second suggested one of the Strepsiptera (Twisted-wings, named after the fact that the wings of the males twist while in flight). These are endoparasites which live in solitary bees and wasps primarily. The females are wingless, so this would be a male. The only problem with this is that the largest they ever get is 4mm in length, and I don't know the size of this one. Also, I have extensively Googled this family, and failed to come up with a match, though found lots of fascinating information. (There are over 400 species)
I'm sorry, Tang, but unless they come up with further suggestions, it will have to remain a UFO.
Could be Drosicha corpulenta (Family Margarodidae).
The picture on the linked page shows a male on the left and a female on the right.
So it's not a fly.
Nice one, Tang. I had been concentrating on the Homoptera, as opposed to the true flies (Diptera), but it is a very complicated group. It certainly looks like a Drosicha sp. (Had not managed to find a pic of a male on the web, only the wingless females!)