Bagford was originally a cobbler, but he became a book collector in his later years, and he assembled this set of ballads from the materials he had been collecting.
Harley was interested in all sorts of antiquarian literature, and the Harleian collection is a major contribution to scholarship.
The Bagford Ballads are generally folk compositions that document the last years of the Stuart reign in the close of the 17th century (a subject that was not remote for Harley).
Therefore, in contrast to what Thomas Percy would collect, these ballads were not primarily antiquarian or efforts at preserving a vanished literature.
After Harley's death, the Bagford Ballads were obtained by the Duke of Roxburge.