This, I think, is a Shaggy Parasol mushroom (Macrolepiota Rhacodes). I've found it's relative, Macrolepiota Procera - Parasol Mushroom) occasionally in the countryside, but never anywhere near our house. Both of these mushrooms are edible.
Can anyone tell me then, why this mushroom was found growing inside our house, albeit in an undeveloped part? It was growing quite happily in the angle between the floor and a plastered wall. I've since broken the cap into various small parts and distributed them around the garden, hoping in future years they may choose to grow here.
In the meantime, I've been busy spinning like mad for our Christmas sale on 1st December in the village hall. There will be photos soon!