Green’s Dictionary of Slang

underhand, deceitful.

1821–6		‘Bill Truck’ Man o’ War’s Man (1843) 292: That smells too much of the Jerry Sneak way of going to work [...] and don’t look like honest true blues at all.
1838		‘Paul Pry’ Oddities of London Life II 260: A STOUT, hearty vender of small wares, of genuine ‘Jerry Sneak’ aspect, made his way into the office.