Barnet, London, December 2017
Yellow Brain Fungus (tremella mesenterica)
These are both most likely tremella mesenterica (possibly tremella aurantia) – this does not actually grow on dead timber, but rather on the crust fungi that covers dead timber, and is therefore parasitic rather than saprobic.
Seen left in its usual bright yellow, and right turning orange as it dries out.
Some sources report this as an edible species (others as inedible, though not poisonous), but being insubstantial and not tasting of anything in particular, it is not considered a desirable mushroom.