The last published key to the British fauna was that of Collin (1958), but 11 species have been added to the British list since that time and there have been many changes of nomenclature which make that key hard to interpret. Collin's key was also largely unillustrated. I have been working on an updated key to the British species for a number of years and it has been tested by many members of Dipterists Forum. The latest version (download as PDF 7.4Mb) was produced for the Dipterists Forum workshop in Feb 2014. This key is extensively illustrated using photographs of specimens.
A very provisional set of maps was also produced for this meetings and is also available for download as a PDF (3Mb).
A more recent version (25/06/2015) includes both maps and phenology plota and is optimised for use onscreen with a touchscreen interface such as a tablet. Download PDF (8.56Mb).