Green’s Dictionary of Slang

(UK Und.) the breast pocket.

1821		D. Haggart Autobiog. 16: M’Guire came to us and pointed out a conish cove, with a great swell in his suck.
1833		‘The Slap-Up Cracksman’ in Swell!!! or, Slap-Up Chaunter 43: So flick the suck — or draw the clicks, / The lil, the jam, or bung from kicks.
1857		‘Ducange Anglicus’ Vulgar Tongue 44: Picking the suck is a kittle job Stealing from the breast pocket is a difficult job. [Ibid.] 45: Three screaves in a lil which I fork’t from a suck Three bank notes in a pocket book which I took from a breast pocket.
1897		C. Whibley ‘The Switcher’ A Book of Scoundrels 211: The breast-pocket [...] is a severer test. ‘Picking the suck is sometimes a kittle job.’.