came across this in longish grass did not stay long ants all over, large mound looked disturbed poss a dog also woodpeckers in area
No interactions present.
Agreed definitely not Lasius flavus. I would stick my neck out and opt for L. niger s. str. L. niger is the only black/brown Lasius which builds large soil mounds (and usually in long-ish grass). Its sister species, platythorax, does not build soil structures. Aggressive behaviour also supports niger ID.
Lat/Lng: 53.6, -1.3
OS grid ref: SE4713