I’ve been taught this tune by my teacher, whose band plays it at gigs. Radstock is a very old town south of Bath in Somerset.
It is a single reel, 8+8 with no repeats. It’s full name is "The Radstock Jig", "jig" in this case presumably being a centuries-old usage referring to lively leaping and jumping dances, and reflects the age of the tune.
The tune is distinctive in that it starts in Cmaj, progresses to G and Amin, and then settles down in Amix.
Last time through it’s nice to play the final bar as |A2A>G A4||, giving a slight Bartokian flavour.
My teacher thinks it’s more of an old set dance than a reel as known today.
This is a version of "Poll Ha’penny". "Jig" meant a solo dance - in this case probably a stepdance - in England, and I suspect James Higgins (from whom Cecil Sharp collected he tune) played it as a hornpipe (but at reel speed in the sounthern English fashion).
Another recording of the tune is on 2005’s "Duck Soup" by the Sussex band of the same name: Dan Quinn, Adam Bushell and Ian Kearey.