Green’s Dictionary of Slang

yennep flatch n.

three halfpence.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1873		Sl. Dict.
1935		R.T. Hopkins Life and Death at the Old Bailey 65: Costermongers invariably use the following terms in discussing money transactions [...] Yenep-flatch – Three half-pence.