It’s the first species that I’ve tried to identify from the Collins Fungi Guide, by Stefan Buczacki and going by his description and the illustration by Denys Ovenden I think this must be Yellow Cobweb, Plebiella sulphurea, formerly known as Trechispora vaga, although I’ll admit that my photograph, taken on the 17th, makes it look more like yellow vermicelli.
Thank you to Monique in the Netherlands who tells me this isn’t in fact a fungus (see comment), I did wonder about that:
It’s called dog vomit slime mold, in Dutch “witch’s butter”. It’s very slimy and it can “walk”.
You can see its slime trail over the moss in my photograph.