Yes - an old puffball.

The response from the British Mycological Society was:
This is the base of a large puffball after the ball has crumbled away. The species is Calvatia utriformis also called Handkea utriformis. It is a locally common species, usually on more alkaline soils I think and can get very large (6 ins across). It always leaves these stumps behind.'
They were very helpful and quick.
I have posted another fungus ID thread.
Susanna