What I think are deer mushrooms, Pluteus cervinus, growing on wood chips. The caps of this species are often a lighter brown colour. The gills look like this:
I took a specimen home with me but was unable to get any spores from it. However, under the microscope the gill surfaces showed the large protuding horned cystidia that are characteristic of P. cervinus (magnification x150, field width about 344um):
A close view of one cystidium (magnification x600, field width about 86um):
First 2 photos and specimen taken in the Wilderness, Whiteknights Park, Reading, UK, on 2013-11-10.