MERIPILUS

This is the fruiting body or bracket produced by the Giant Polypore, Meripilus giganteus.  A mass of overlapping fronds, which may be up to 60cm across.

  

This fungus favours beech trees, though it will occasionally appear on oak, plane or monkey puzzle trees.  It appears at ground level or even above roots some distance from the tree.

On beech it renders the wood at the base of the trunk brittle and is therefore rather dangerous.  Once the brackets appear, the decay has been going some time and a strong wind could bring the tree down, especially, as with the tree in the picture, if the winter wind resistance is increased by a lot of ivy. 

The red goblin gives an idea of scale.