To Eat or Not To Eat . . . That Is The Question

Finally got out into the garden today - the rain actually stopped for long enough to allow us to cut the grass (which was getting a little out of hand to put it mildly). Got a bit of weeding done as well - Martin found the following under the Yew tree - the question is whether they are edible or not . . .

Anybody got any idea? Tried to identify them, think the white gills might be a bad thing . . . So I gues the answer is 'Not To Eat' this time . . .