Cinnamon porecrust fungus, Phellinus ferreus, growing on a decaying trunk of a birch tree (Betula sp).
I took a sample to examine more closely back at home. It showed about 4 pores per mm:
The above sample did not yield any spores so I took another a few days later. This following image (x600, image width 86um) shows spores from this second sample:
These spores are about 6.5 - 2.5um which agrees well with the 5–6.5 x 2–2.5um quoted at Roger's Mushrooms.
First photo and first sample taken in the Wilderness, Whiteknights Park, Reading, UK, on 2013-02-05. Second sample taken in the same place on 2013-02-08.