Thanks Igor. Previously HK has recorded 3 species of Medetera, namely M. austroapicalis, M. grisescens and M. opaca. Thus there is a good chance that the above fly is indeed M. grisescens.
We had another specimen of Medetera caught on 14.vi.2012 from the same locality. Do you think it belong to the same species as the first one in this post or a different species of Medetera?