Scottish Environment Protection Agency
Probably one of the best designed official sites: contains all sorts of up-to-date material, an education section, and interesting historical statistical data.
The equivalent to the Scottish site: lots of free and useful information and data.
An enormous list of links to just about every environmental law issue and country. Last updated in 2013.
Friends of the Earth Scotland
Campaign group, contains a lot of information about the work of the campaigns and a limited amount of information about the legal issues.