On a log of very old and rotten Scots Pine.
The first clue is its athelioid nature, an indeed it was considered an Athelia before. You can see the soft webbiness of the fruit "body" in the first pic and the fact that it has slight holes through it. Another thing this has revealed is what Ellis and Ellis mean in their key by "not firmly attached to substrate". This is the first species I have keyed out there which follows this route. It's the only species in Ellis&Ellis of this genus, though there are others listed in Bernichhia.
Everything about this fungus is tiny, so that even at x1000 with oil you are peering hard. The hyphae are barely 2u wide, the spores not much more than 2u long