I don't recognize it as a folk tune, but thanks for posting. It's a good tune.

The page you linked, Runrig Fan, led me to a version by Ella Fitzgerald. I'm struck by the differences between the present-day video and the old one. The video of the present day features unhealthy-looking young people looking creepy while being vaguely threatening.

The old one simply shows Ella's face, looking charming. I won't get started on the horrors that the people of 1939 were facing.

Makes one wonder, don't it?