Confidence: I'm as sure as I can be.
Notes: A characteristic peatland species, and a lichen! The granular, green algal mat contains fungal hyphae and is the thallus of the lichen, and the toadstool is then the fruiting body. Very variable in shape, but we can see the matt (minutely pruinose) stem, and the younger specimens show the red-brown flush right at the top of the stem, very characteristic of this species. One of the few lichens that are formed by a basidiomycete fungus rather than an ascomycete. I have all the British Lichenomphalia species on my lichen website - see http://www.lichens.lastdragon.org/Lichenomphalia_umbellifera.html and adjacent pages. My photographs show rather more delicate, elegant specimens, but it is often chunky as shown here. Alan