A pale cup fungus, probably a Peziza sp, growing on a beech log (Fagus sp). It was about 5cm across.
I took the following specimen home with me:
This yielded the following spores (magnification x600, field width 86um):
These are about 15 x 7.5um.
First photo and specimen taken in the Wilderness, Whiteknights Park, Reading, UK, on 2014-01-11.
Probably Peziza repanda.