Field Studies Council (FSC)
FSC run a wide variety of Natural History courses at their field centres spread throughout the nicer parts of England and Wales.
FSC also publish identification handbooks (including the highly accessible "AIDGAP" series) and they have taken over the professional-level "Synopses of the British Fauna" from the Linnean Society. They also act as agents for the Royal Entomological Society Handbooks (also professional level).
Some FSC publications are downloadable under a Creative Commons Attribution-Noncommercial-No Derivative Works licence.