Green’s Dictionary of Slang

gerry n.1

[ety. unknown; DSUE suggests Lat. gero, I carry. Note Devon dial. gerred, bedaubed, filthy]

excrement; thus imper. gerry gan, be quiet.

[UK]Harman Caveat for Common Cursetours in Viles & Furnivall (1907) 86: Gerry gan, the ruffian clye thee. A torde in thy mouth, the deuyll take thee.
[UK]Groundworke of Conny-catching n.p.: [as cit. c.1566].