When first seen was a single plant in a marshy place, which was turned into a pond a couple of years ago and plant is now spreaading.
No interactions present.
I'll be back there in May so, if it is flowering then, I'll be able to have a closer look. But I don't have a copy of Stace ... just looked it up on Amazon and it's quite expensive, but maybe I need to go for it. Will consider.
Lat/Lng: 58.0582, -5.4245
OS grid ref: NB980128