This is something I've been interested in a while but have had trouble finding relevant reading material. With so many Mayday/Green Man festivals around in England, it's hard to know where the 'real' history ends and the invented/romanticised traditions begin.
Searching for books through online retailers tends to return either books about folk music or '1001 Pagan spells you can try at home'. Just to clear, I'm interested in the history of folk beliefs, seasonal festivals, Paganism etc; I'm not a believer in it.
I heard Ronald Hutton on the BBC's excellent Making History programme on Radio 4 and have ordered 'The Rise and Fall of Merry England'. Any further suggestions would be gratefully received.
Jacqueline Simpson (1930 - ) is an excellent folklorist and a good place to start - although she specializes in oral tradition more than folk practices. For the latter, her Oxford dictionary with Steve Roud, A Dictionary of English Folklore, is an excellent sourcebook with engaging, informative articles.