Growing in a hollow of a huge sweet chestnut tree.
Edit: 'Coprinellus disseminatus aka Trooping Crumble Cap, Fairy Inkcap, Fairy Bonnets' - thank you, Geograph member 'marshman':
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Edit: 'but they are not ink caps. They are so-called because the black spores make an 'ink' when the gills autodigest - there is no sign of this in your fungi [see, for comparison
NO5102 : Shaggy Ink Caps, which shows various stages [different species, but the principle is the same.]]. They are Mycena [a Bonnet of some sort - I hate the contrived English names and have never become familiar with them] -there are a few clustered species like yours on wood, but I would not try to identify from a photo. M.inclinata went through my mind, but I would not be certain - it is common on oak, but less often on Sweet Chestnut and rare on Beech. I would not be more precise than a clustered Mycena on Sweet Chestnut, perhaps M. inclinata' - thank you to Geograph member M J Richardson
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