kate and sidney, n. — Green’s Dictionary of Slang

kate and sidney n.

also kate and sydney

[rhy. sl.]

steak and kidney.

[1907		Barrier Miner (Broken Hill, NSW) 21 Sept. 3/4: An excited young mother opf twins [...] when asked what names they were to have, replied ‘steak and kidney’ instead of ‘Kate and Sydney’].
1914		W.L. George Making of an Englishman I 68: ‘You better have a Kate and Sidney,’ said Maud; ‘it’s English, quite English, you know.’.
1971		J. Jones Rhy. Cockney Sl.
1980		(con. 1930s) Barltrop & Wolveridge Muvver Tongue 21: Kate and Sidney: steak and kidney.
1998		R. Puxley Fresh Rabbit.
2001		Interior News (Smithers, BC) 28 Nov. C4/3: I did, however, like steak and kidney pie, or Kate and Sydney as I call it.