Purcell was a bit of a folkie, adapting & arranging all sorts of traditional material - including Scottish stuff. He might have come up with original tune for Mad Tom of Bedlam which no one does anymore in favour of the new one. Not folk as such but it shiows the exgtent to which he was familiar with such things. Of course Purcell predates much of what we think of as being Traditional by 150 years, so the key traditions are still in place in Choral Evensong, only broken by the republican intermission.