A few days ago I noticed some of these on a pile of wood-chips in the woods between Farnborough North and Frimley stations. I also noticed that they seemed to change form between the mornings and the afternoons. I have tentatively identified them as Coprinus lagopus, a type of ink-cap mushroom. In the mornings their stems are straight (up to 12cm long) and their caps neat little inverted translucent grey umbrellas (up to 5cm across), as shown above. By the late afternoon, the stems have drooped and the caps are ragged, shrivelled and blackened, as shown below.
However, by the afternoon, the next day's mushrooms are already thrusting their heads up: