Green’s Dictionary of Slang

1. a fiddle.

1960		J. Franklyn Dict. of Rhy. Sl.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 31: Hey Diddle Diddle Fiddle.
1992		R. Puxley Cockney Rabbit.

2. the middle.

1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 31: Hey Diddle Diddle [...] middle.
1992		R. Puxley Cockney Rabbit.