Green’s Dictionary of Slang

(UK Und.) an imitation gold coin, a fake sovereign; also dandy-master, a forger of gold coins.

1883

J. Greenwood Tag, Rag & Co. 24: She receives in exchange for the ‘dandy’ the spirits and seventeen and sixpence. [Ibid.] 24: The spirits [...] find a ready sale at public-houses known to the ‘dandy-master’.