The British species were treated by Phil Withers in 1989 in the fourth issue of the Dipterists Digest. This can be accessed here: https://www.dipterists.org.uk/sites/default/files/pdf/Dipterists%20Digest%201989%20series%201%20no%2004.pdf
Since Wither's publication there have been changes to the nomenclature of genus Psychoda and additional species found in Britain. The following key takes most of these into account. The key includes photographs taken by me to help illustrate features.