For anyone interested the best place for information about dry stone walls is the The Dry stone walling association of GB.
http://www.dswa.org.uk/
There is also a fantastic practical handbook on walling from the BTCV.
http://www.btcv.org/
If you want get involved in walling conservation there are opportunities through the BTCV.
Courses in walling are run at Craven College in Skipton.
http://www.craven-college.ac.uk/