General insect identification books

As a general introduction to insect identification, Michael Chinery's field guides are hard to beat - they contain a wealth of information and lots of good pictures. For almost any insect you find Chinery will help you find out which group it is in, but be very wary of using Chinery alone to identify to species level - the field guides show less than 5% of the British species (plus quite a few continental species that aren't in Britain), so don't pretend to be a comprehensive guide to species identification. There seem to be three versions available at present:

• Chinery, M. 2007. Insects of Britain and Western Europe (Domino Field Guide). A&C Black. [The best-illustrated one for identification.]
• Chinery, M. 1993. Insects of Britain and Northern Europe (Collins Field Guide). Collins. [Very good text with some keys to main groups, but fewer illustrations.]
• Chinery, M. 2005. Collins Complete British Insects. Collins. [No more "complete" than the other two, and illustrated with photos which are less useful for identification, but the focus on Britain makes it simpler to use.]

There are excellent keys to the main groups of insects and other invertebrates in the Field Studies Council series:

• A key to the major groups of British terrestrial invertebrates
• A key to the major groups of British freshwater invertebrates
  

FSC also do a whole range of introductory fold-out charts for various insect groups.

Insects feature on lots of websites of course (see Kitenet's insect links), although I haven't yet found one that does a good job of helping you to identify what type of British insect you're looking at.

Good societies to join include the AES and BENHS.