Cannot really be sure of the species, but potens is probably unlikely. The side of sternite 3 looks shiny rather than dull if I had to choose between the two.
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Very jealous...not a species we see up here! Good set of photos, too.
My Flickr photos...
Lat/Lng: 51.1911, 0.2448
OS grid ref: TQ569459
In herbaceous vegetation opposite pond dipping platform.