I first found this fungus last week and went back today to get more photos. It had me flummoxed at first – it looked mazegill-ish but is growing on a handrail so I couldn’t identify the wood and couldn’t match the fungus to anything in my books. Fortunately, there are some extremely knowledgeable fungi experts around who are generous with their assistance and one in particular, Andy Overall, was able to identify this from my photos.
This is Conifer mazegill – its scientific name is a bit of a mouthful, Gloeophyllum sepiarium – and it’s a wood-rotter, feasting, as the name implies, on the dead wood of conifers.
The examples I’ve found are very young and don’t look anything like the stiff brackets they will grow in to, though the Mushroom Expert website has one image of this early stage, and a lot more information if you’re interested.