Coincidentally, I too saw my first hoverfly of the year today. It was a drone fly Eristalis tenax in Sane Copse, Yardley Chase. I am sure this mild spell will bring more out. Meliscaeva auricollis is another species that overwinters as an adult so can be found once we have some mild, sunny spells.
The winter months are the time to catch up with unidentified specimens from the previous season and I have been doing just that. Two less common species have turned up in the samples I looked at this week. One was a long-legged fly Dolichopodidae, found at Ditchford Lakes and Meadows in early July. The species was Poecilobothrus principalis. The closely related P. nobilitatus is a very common doli fly where the males display to the females on pondweed by flicking open their white-tipped dark wings and hopping from one side of the female to the other. P. principalis is much scarcer as can be seen from the NBN Gateway map - https://data.nbn.org.uk/Taxa/NBNSYS0000012641/Grid_Map
It seems to be a coastal species from the map but a number of primarily coastal species have been found in the Nene Valley.
The second uncommon species was the Scathophagid fly Cordilura aemula. Details of the species can be found on Stuart Ball's excellent Scathophagidae Recording Scheme website at http://scathophagidae.myspecies.info/scathophagid-checklist/cordilura-aemula
This was found at Abington Meadows, Northampton in September. Its distribution is mapped here https://data.nbn.org.uk/Taxa/NBNSYS0000030370/Grid_Map
I still have quite a few flies to identify from last year so I am hoping to turn up some more interesting species.