Flying around the riverside, near wet boggy areas, waiting for the buds to open.
No interactions present.
Probably B.pascuorum, it doesn't look "bright" enough for either B.muscorum or B.humilis but, as you say, probably not possible to get a definate ID form these two photos.
Tachinid Recording Scheme
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Lat/Lng: 51.796765702234, -3.6892175674438
OS grid ref: SN836122
Nant Llech (SSSI), the woods behind Wales Ape and Monkey Sanctuary, near Henrydd Falls.