Green’s Dictionary of Slang

a deliberately down-played rejoinder, an excl. of positive affirmation.

1853		Dickens Bleak House (1991) 280: ‘I appeal to our mutual friend Smallweed whether he has or has not heard me remark that I can’t make him out.’ Mr. Smallweed bears the concise testimony, ‘A few!’.
1864, 1867, 1870		Hotten Sl. Dict. 132: Few used in a Slang sense thus: ? ‘Don’t you call this considerably jolly?’ ‘I believe you, my bo-o-oy, a FEW.’ Sometimes the reply is, ‘just a few.’ Another expression of the same kind is rather.
1896		W.C. Gore Student Sl. in Cohen (1997) 19: few adv. Used in place of little. ‘Are you sorry to leave?’ ‘A few.’.