I am struggling to identify this one. There were several, well spaced, in grassland around specimen trees in suburban London.
They are about 5 inches across, sturdy and low to the ground and have a really deep crater on top. Some that had been kicked over look rather trumpet-like in shape. The gills were mid-brown.
The shape looks like some of the milk-cap types in my book, but that's as far as I've got.