Green’s Dictionary of Slang

completely, very much so, directly.

1810		C. Dibdin Yngr Songs in the New Comic Pantomime called Bang Up! 16: And bang up he’ll get the whip hand of the town.
1821		‘A Real Paddy’ Real Life in Ireland 61: Every thing that will swim has left the Liffey bang-up full of company to see the sight.
c.1825		T. Jones ‘The True Bottom’d Boxer’ in Egan Bk of Sports (1832) 74/1: He’s always in twig and bang up for the game.
1856		Abbeville Banner (SC) 19 June 1/5: Button up his lip and knock him bang-up!!
c.1930		(ref. to late 19C) N. Kimball Amer. Madam (1981) 13: I was bang-up proud of the place.
1951		A. Buckeridge Jennings Follows a Clue (1967) 101: Here we are, bang up to the eyebrows in the most supersonic hoo-hah we’ve ever struck.