Green’s Dictionary of Slang

(UK Und.) highwaymen who go out robbing in pairs.

1781		G. Parker View of Society II 163: Chosen Pells are companions who ride in pairs. They shoe their horses with leather, stop coaches in town, strip ladies, take down their hair, and extract the jewels from their heads, &c. besides taking their purses, &c.
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Chosen Pells Companions who ride in Pairs, they shoe their Horses with Leather, & Rob Coaches in the Streets of London.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Chosen Pells Highwaymen who rob in pairs, in the streets and squares of London; to prevent being followed by the sound of their horses shoes on the stones, they shoe them with leather.
1871–82		B.M. Carew Life and Adventures [as cit. 1788].