This site is maintained by Jon Maynard FRICS a chartered land surveyor specialising in boundary and other problems between neighbours. Lots of practical advice.
This site is currently being updated but it still has a discussion forum and summaries of cases relevant to party walls. There is also a link to the Pyramus and Thisbe club, the organisation for professionals specialising in party wall matters.
Has some useful information on roots, trees and bonfires etc. It also has a lively discussion forum which contains some interesting questions and answers.
