Confidence: It's likely to be this, but I can't be certain.
Notes: Keyed out using Stubbs and Falk
Tribe: Upper outer cross vein not re-entrant, R4+5 straight, no terminal arista, no plumose arista, no shaggy hair on face, inner cross vein before middle of discal cell, face with central prominence, arista much longer than 3rd antennal segment, abdomen not flat and dull on top with orange side patches, no distinct eye margin, distinct colour pattern, black face (Bacchini).
Bacchini: Body not waisted, smaller species, parallel-sided abdomen, wings 5-8 mm, male (eyes touching on top of head), front tibia and tarsus cylindrical, abdomen with orange spots on at least 2 tergites (Melanostoma)
Tergites 2 and 3 not quite 1.5 times as long as wide (hence not a definite M. scalare) but neither are they as long as they are wide...
Frons angle not more that 90 degrees, frons shining. Face narrow. Suggests M. mellinum, but abdomen NOT strongly widening posteriorly and sternites NOT extensively pale.