Steve and Noreen - very *very* much appreciated, thank you for taking the time.

I've discovered that giglot is 14th c. term for a lewd, wanton woman, obscure origin, so gig in the sense above must be an abbreviation of that.

Peg a (also Peggy and Peg o') Ramsey or Ramsay is much older than Pills to Purge, being named as the tune for some 17th century broadsides. It must have been very well known indeed in c.1600 when Shakespeare used the song title - with the audience intended to know exactly what it implied - in Twelfth Night:

Sir Toby Belch: My lady's a Cataian, we are politicians, Malvolio's a Peg-a-Ramsey

Now whether D'Urfey reproduced what was already extant, added to it or simply rewrote the whole thing, we can't know, but the latter seems unlikely given the way it fits in Twelfth Night. If D'Urfey did rewrite the whole thing he almost certainly did it in the spirit of the original, just as the broadside The little Barley-corn was a rewrite of Stingo, with different words but exactly the same meaning. Unless you know otherwise ...