At high altitude amongst Salix herbacea and Carex bigelowii in acidic turf.
No identification made yet.
No interactions present.
You have given the nearby trees and type of soil which is good. Unfortunately, and I know it is probably too late for some of your observations, to make identification possible we need more information. A photo of the gills and the stem showing their colour and if the fungus has a ring all helps. It still does not guarantee id but would go a long way.
Lat/Lng: 56.54457, -4.22025
OS grid ref: NN635413