Green’s Dictionary of Slang

a character, also used of children.

1950		C. Harris Three-Ha’Pence to the Angel 21: Not much of a bunk – you’ll have to share it with one of the herbs. [Ibid.] 100: You ’erbs, I suppose yer know where you’re going, don’t yer, time you was orf ter Sund’y School.
1953		J. Franklyn Cockney 286: ‘A lad’ in cockney slang means simply a witty, impertinent, or daring, person of either sex. [...] It is synonymous with a one, a card, a caution, a cough-drop, and very largely with an ’erb.