Thanks for that Sian, I did a quick search but possibly didn't punch in the right words.

A.L. Lloyd's 'Folk Song in England' - looks like that one's been recently reprinted. And may offer the kind of detailed information which will help me know what all the arguments on here are actually about! Some of the others mentioned here look as though they have been so well loved that there's virtually no volumes out there. A trip to the library perhaps...

Now I better check that permathread. And try to be a very good girl at Amazon....