The Wildlife and Countryside Act 1981 includes a number of fungi in Schedule 8.  All of these designations are also available in the Species Designations Database.  It is an offence to pick, uproot, trade in, or possess for the purpose of trade, any of the designated species.
Fungi are very poorly represented in international legislation.  Six species of lichenised fungi are included in Annex V of the EC Habitats Directive.  These designations are available in the Species Designations Database.  Annex V includes those animal and plant species of community interest whose taking in the wild and exploitation may be subject to management measures.  This is described in Article 14 of the Directive.  The UK is required to conduct surveillance of the conservation status of species included on Annex V, and to use this surveillance to inform whether extra measures are necessary.  The UK is further required to report on the conservation status of Annex V species every six years.
In addition, the lichenised fungus Cetraria islandica is included on Annex D of the EC CITES.  This requires import notifications to be provided.