Don't know which 2 Steve meant, of course, but I would reckon 2 folk revivals --

1 about 1890 -1920s --- Baring Gould, Kidson, Fuller Maitland, Lucy Broadwood, Sharp, the Hammonds, Gardiner, Gavin Greig, Alfred Williams, Moeran, RVW, Grainger ...

2 1950ish+ Lloyd, MacColl, Lomaxes, Seeger, Ritchie, Kennedy, Palmer, ++++++++

I knew about those. :-)

I wonder if there is not a third - going on at the moment, its major feature being a new look at old music with a greater mix, but instrumental based. I can certainly make a case for this.