Green’s Dictionary of Slang

1. the stomach.

1932		‘P.P.’ Rhy. Sl. 9: A clip in the ‘Newingtons’ will do him a bit of ‘Robin Hood’.
1938		F.D. Sharpe Sharpe of the Flying Squad 332: newington butts: Guts (‘That tale gave me a pain in the Newingtons.’).
a.1945		L. Payne private coll. n.p.: Stomach (Guts) Newington Butts.
1960		J. Franklyn Dict. of Rhy. Sl.
1969		S.T. Kendall Up the Frog 12: This ’ere bloke grabs ’im by the ’oller boys ’oller and gives ’im a real fourpenny one in the Newington Butts.
1979		R. Barker Fletcher’s Book of Rhy. Sl. 21: Her hobsons, low and husky / Made my newingtons go numb.
1989		J. Morton Lowspeak.

2. (UK Und.) courage.

1959

J. Gosling Ghost Squad 25: Thieves’ argot, spoken properly, is a foreign language which needs to be learned [...] Among the words and phrases derived from rhyming slang: [...] ‘He's got Newingtons’ means ‘he's got guts’ from Newington Butts, a district of London.