Green’s Dictionary of Slang

at once, unquestioningly.

1821–6		‘Bill Truck’ Man o’ War’s Man (1843) 139: I can answer you for him slap off the reel.
1902		Wodehouse Pothunters 39: ‘[H]e wouldn't send me two quid off the reel without wanting to know all about it’.
1913		Truth (Sydney) 27 Apr. 11/3: This werry fast young feemale / [...] / Went clean off her daisy rocker / On him, right bang off the reel.