I believe there was a project a few years ago to record all the remaining WW2 coastal defences. I can't remember its name, but no doubt someone here will
Simon - I suspect that you are thinking of The Defence of Britain Project, which ran from April 1995 to March 2002 under the auspices of the Council for British Archaeology. Nearly 20,000 twentieth century military sites in the United Kingdom were recorded by an army of some 600 volunteers. The final report on the project is now available online.