Green’s Dictionary of Slang

the penis.

1882		Cremorne II 51: He took his short fat kerp in his hand.
1882		Cremorne II 52: His hand with passion shook; / Then it stole along and sought the shaft / of his kirp so long neglected.
1976		D. Ireland Glass Canoe (1982) 115: The Darkfella had a kerp like no one else. It was fairly long and very thin. When its mind was on nothing in particular he could tie a knot in it.
1998		R. Puxley Fresh Rabbit 47: The widely known Hampton Wick, for what in backslang is the ‘kaykirp’.