Dolichopodidae: Hydrophorus albiceps?

I agree with Martin's identification. The only other British contender is rufibarbis whose face is the same brown or slightly golden colour all over, but albiceps has a few short but obvious setae on the mid and hind femora (almost absent in rufibarbis). You cannot see another good character, which is the rather undistinguished ventral hairs on all the femora in this species, but which in rufibarbis are clearly longer (up to half the femora depth) and more upright and often pale. And, as Fonseca says, the front coxa hairs are black, at least on the outer face (not 'entirely' as he incorrectly says), compared to all yellow and much longer in rufibarbis.

All my albiceps (and rufibarbis) females have rich dark brown dusted frons, not a hint of silver.

H.albiceps is mainly found in Scotland (but we have it on Dartmoor) so Islay is spot on.

Thanks Martin, a new species for me, and one that was great fun to watch skimming over the dark peaty water in the company of whirligig beetles and pond skaters.