Most of the information given so far is on English Folk Song. However if you are studying British folk song, then you can't leave out the contributions of the Scots, Welsh, and Irish. England and Britain are NOT synonomous terms.

Check out the School of Scottish Studies in Edinburgh, and you need to also check out the significant contribution made by the travelling people. In Scotland, you need to look at the late Jeannie Robertson, her daughter Lizzie Higgins and her nephew Stanley Robertson. The Stewarts of Blair, are important, as is Elizabeth Stewart from Aberdeenshire. Sadly, only Sheila Stewart remains of the Stewarts of Blair, while Stanley and Elizabeth are both still alive.

You could also find more information on the website of the Elphinstone Institute, Aberdeen University. I'm not sure of the web address, but google it.