Green’s Dictionary of Slang

ecnop n.

a ponce.

1932		T. Croft Cloven Hoof 41: There are centuries-old words used in the criminal classes [...] ‘ecnop’ or ‘ponce’ for prostitutes’ male assistant.
1956		‘Charles Raven’ Und. Nights 24: But at least it’s saved Iris from that dirty little ecnop, Ronny.
1966		Trimble 5000 Adult Sex Words and Phrases.
1986–7		Maledicta IX 144: Few have a ponce (pimp, backslang ecnop).