Steve Gardam kindly referred me to the work of Roger de V Renwick, an American writer on folklore. I found a piece of his on servants in Child Ballads. I though this might be an interesting topic. Questions posed via De Renwick's piece include the following:

Servants do appear in ballads but are rarely the heroes or heroines. Why?

"Many Child ballad servants are unable to think for themselves". Is this a fair statement?

If, as has been assumed, ballads were principally a 'working-class' cultural possession (his words not mine) how come servants get a bad press in so many ballads (my words, his idea)?

I found the piece on JSTOR. Stable URL: Stable URL: https://www.jstor.org/stable/j.ctt46nrm0.10

It comes from a book called 'The Flowering Thorn'.