A toothed crust fungus, probably Basidioradulum radula, growing on the fallen branch of a broad leaf tree, probably oak.
I took the following specimen back home with me:
This yielded the following spores (magnification x600, field width about 86um):
These spores are about 7.5 x 2.5um which is a little smaller than the ranges of about 8-12 x 3-3.5um usually quoted for B. radula.
First photo and specimen taken in Whiteknights Park, Reading, UK, on 2013-12-24.