Coming in from a different and wholly non-professional angle:

My public musical experience comes almost entirely from the "filk" community arising out of science fiction/fantasy fandom, and from that community's long-standing tradition of holding open song circles (both at private homes and at conventions). It should also be noted that the filk community quite deliberately encourages participation based on enthusiasm as opposed to talent or polish. I do not count myself as anything resembling a professional-quality vocalist, but when I can keep myself on-key I'm good enough not to embarrass myself in a circle that does include a fair number of properly trained performers.

Also relevant in my case: whereas my formal musical training ended in junior high, I was active in speech and debate through college and also counted stage magic as a hobby while growing up.

With that background: if you see my hands moving while I'm singing, one of two things is going on, and one of those absolutely is "conducting myself". If I'm gesturing consciously -- which I may be, given my speech training, particularly if I'm trying to sing "in character" -- those gestures will almost certainly correspond in some respect to my vocal rhythm. If I'm gesturing unconsciously -- which I also may be (see "purely amateur at this" disclaimers above) -- then the gestures will also correspond to the vocal rhythm, because it's far easier for my hands to work with that rhythm than to work against it.

And in a song circle, I may very well also be doing a little bit of audience-conducting -- possibly because I'm hoping for help on the choruses, very infrequently if someone's jumped in with an instrument to back my vocals, or as treewind notes above, to mark the end of a final chorus.

All of which may have very little to do with trends in up-and-coming British folk performance. OTOH, if the performers involved have been largely self-trained and have spent much time leading song circles around campfires or for church youth groups, etc.,....