You are correct that it is a fly (Diptera).
Identification of (most) flies is a question of tiny tiny details - like the presence or absence of a certiain bristle or the shape of a vein in the wing, and is far beyond the capacity of common mortals like me.
Yep it is a fly...but as has been said pretty difficult for ordinary amateur to id..but its raining so i looked into it and am pretty sure this is a member of Lonchaeidae...given the 'broad rather clear wings' and i quote 'the marked break in the costa near veinSc.' as seen halfway up on the right edge of the right wing in your pic. Glad you asked? Not an id but close i think.
Lonchaeidae should have the halteres black - to me, it (or at least what I think is the halteres) looks yellowish in the photo. Also Lonchaeidae should usually be black or metallic blue.
To, for instance, separate Lonchaeidae from Scathophagidae in my key one has to check whether it has a lower fronto-orbital seta or not - which I can't tell from the image. Now, I in no way say that it belongs to Scathophagidae, just that it doesn't seem to fit in Lonchaeidae.
And to me it looks like it is laying eggs in some dung, which I think shouldn't fit with Lonchaeidae.
Personally I think it looks quite a lot like a Coenosia sp. (Muscidae), image of a wing here, or something related - but, to be true, I really have no idea. Flies are impossible!