Green’s Dictionary of Slang

rolls royce n.

the voice.

1960		J. Franklyn Dict. of Rhy. Sl.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1981		P. Wright Cockney Dialect and Sl. 105: Rolls Royce ‘voice’.
1992		R. Puxley Cockney Rabbit.
2002		M. Coles More Bible in Cockney 12: Shout with a loud Rolls-Royce. Don’t be scared.