It's not one we get much round here so I would not like to say for sure but Leucoagaricus leucothites would seem the best guess.
A few general points with this.
1.
Small White Jobbies Very difficult to properly identify these and generally ones to
avoid unless you are certain because of the real danger of potentially deadly poisoning. Your specimen is large and you give a good photo or two which is handy (especially the tape measure!) which helps but something I would be reticent to ident just from a photo.
2.
'If In Doubt Leave It Out'. In other words if you are not sure don't pick it! and that means avoid putting anything you are not sure off in your basket. If you do and discover it is toxic then you have to trash the whole lot, and even if you pick them out small bits can break off etc. Never worth the chance.
3. Beyond safety reasons, I think we should
avoid picking
wild wild plant unless it's use will serve a purpose i.e. eating. Get a small handy identification book preferably with a cloth cover so you can
take the book to the fungi, not the fungi to the book
Seriously, mushroom foragers get a bad name with mycologists and sometimes for good reason. Everytime we walk over the soil we compact the ground and if this happens too much this can damage and kill the mycelium growing invisibly so not only should we be careful when picking fungi, we should leave those we do not intend to eat for others to enjoy and for them to release their spores and provide a food source for insects etc.
In France you often see any 'toxique' mushrooms knocked over or stamped on in a old fashioned attitude to destorying anything that may harm humans. It breaks my heart to see and I do try to re-educate the kids who forage with us. It is so much nicer to leave these, often beautiful works of nature for others to enjoy. They are often good indicators for edible species too.
So please try to avoid picking fungi unless 'absolutely' necessary for ident purposes (photo detail, spore prints) and then only if there are plenty around (which is not often the case).
4.
The Wild Mushroom Pickers Code Of Conduct. Check out this pdf guide available for free/ download from the British Mycological Society web site. Direct link here:
http://www.britmycolsoc.org.uk/files/Pickers_code.pdf
Really worth taking a small digital camera on mushie hunts and the small ident book. here a a few suggestions of the better POCKET size guides:
I use:
The Photographic Guide to Identify common and important Mushrooms
Roger Phillips. 1986. cloth cover. Elm Tree Books/ Hamish Hamilton Ltd. ISBN: 0-241-11756-9 Pbk
His great photographic guide in pocket form. Not so easy to find now but if you do get it. There are a few other pocket size versions of this book around under other titles, as well as the full size book which is perfect for keeping at home.
Other Good Pocket Size Guides for UK & Europe
Field Guide to Mushrooms of Britain and Europe
H. Grunert, Renate Grunert. Paperback 288 pages. 1991. The Crowood Press. ISBN: 1852235926
I like this series of books (I have it for Butterflies of Europe and Orchids of Europe). Usually good photographs, illustrations and lots of detail both of edible and toxic species.
Mushrooms and Toadstools - Collins Gem Series
Patrick Harding. Paperback. 256 pages.1999. Collins. ISBN: 0004722701
Smallest of the lot so easy to drop in the pocket or rucksack (like their other bushie related books) and cheap but still a good guide, nice photos and describes over 230 species.
For some reason Amazon.co.uk has it at a high price but you can get it for around £3.95 or £3.19 new from here:
Countryside Book Shop
The Easy Edible Mushroom Guide
David Pegler. 256 pages. 1999. Aurum Press Ltd. ISBN: 1854106317
I do not have this book but it is very well regarded and on of the more up to date books. Well worth a look, especially given this ringing endorsement from amazon.co.uk:
An excellent and very useful guide.
I haven't died yet!
Finally if you prefer colour line drawings,
Pocket Guide to Mushrooms and Toadstools of Britain and North-West Europe
Marcel Bon. 368 pages. 1200 colour illustrations. Christopher Helm. ISBN: 071367458X
This is also a well respected guide and noted for it's lovely illustrations. The reprint is due in March 2006.
From the publisher's announcement:
`Superbly illustrated, highly informative, the best kind of field guide. Mr Bon has given us an excellent and beautiful book.' Dr Roy Watling, past President, British Mycological Society
This guide to over 1500 reasonably-sized species with gills or tubes covers all those that are likely to be seen in Britain, Ireland or in Europe north of the Alps and Mediterranean zone. It is fully keyed, and illustrated throughout with scrupulously accurate colour paintings and spore drawings.
Descriptive text details colour, form, taste and small. Frequency information is given for the British Isles and edibility (or poison) is always made very clear. This book has been completely revised for this edition.
Above all, try to find someone who knows what they are doing, either via BCUK Meet Ups, Local Wildlife organisations or local mycological societies (check out the
British Mycological Society for details in your area)
Happy (Safe) Fungi Foraging