Regarding Pseudonymous's question about modes, the Edwardian collectors and later revivalists like Lloyd did get rather over-excited by the concept, especially by the regular occurrence in collected melodies of scales that weren't the regular major.

What we know now, thanks to the availability of many sound recordings from which we can make our own judgements, is that the intervals that define the different modes (i.e. the flattening of the sevenths, thirds and sixths) are often precisely the intervals that traditional singers pitched with a degree of ambiguity. So to try and force every melody into a modal category like 'dorian' when the thirds or sevenths may be either flat or sharp within a single verse, or possibly hit on the quarter-tone, is to over-simplify a complex phenomenon.

A further issue is that early collectors like Sharp (and Lloyd in Penguin 1) expressed a bias towards non-major tunes. Roud and Bishop's Penguin 2 tried to correct this - but that had the result that some folkies found a lot of the tunes rather bland since so many of them were major.

Personally I love my Mixolydian and Dorian, and am almost certainly biassed towards them in my own song selection, but then I'm a product of the Folk Revival and not a country pub singer of the 1920s.