From a few days ago: a bleeding crust fungus, either the bleeding oak crust fungus Stereum gausapatum or the bleeding broadleaf crust fungus, Stereum rugosum. As it was growing on an oak log, I suspect the former, but my inexperience means that I cannot exclude the latter.
The following is a photo of what I presume is the same species from back in January:
This specimen wasn't bleeding.
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2010-12-12 and 2010-01-28, respectively.