#1
Is this
Hydrotaea armipes please? UK. Woburn, Bedfordshire. 13 June 2022. [name used by Fonseca. Now
H. floccosa Macquart, 1835. Corrected thanks to Nikita Vikhrev].
#2
I guess you used Fonseca's book. You found correct species but incorrect name. After examination of type material (mostly by Adrian Pont, who was Fonseca's student being young) several names have to be changed by priority and nomenclature reasons. Mark in your book:
Hydrotaea occulta sensu Fonseca or Hennig is now
H. armipes
Hydrotaea armipes sensu Fonseca or Hennig is now
H. floccosa Macquart, 1835, which is correct name of your fly.