Here are some links to other organisations which you may find useful:

Fungus Conservation Trust (formerly the Association of British Fungus Groups)

Fungus.org.uk

The British Mycological Society

BMS List of Fungus Groups

Cotswold Fungus Group (see also their Facebook page)

Herefordshire Fungus Survey Group

Worcestershire Fungus Group

North Somerset and Bristol Fungus Group

Gloucestershire Wildlife Trust

Gloucestershire Naturalists’ Society

Natural England (formerly English Nature)

Checklist of British Fungi

Bioimages

i-Spot (photo identification)

First Nature