Green’s Dictionary of Slang

(UK Und.) a gentleman’s house, thus potentially good for begging.

1845		G.W.M. Reynolds Mysteries of London vol. 2 142: Nibsomest cribs Best houses.
1864, 1867, 1870		Hotten Sl. Dict. 187: nibsomest cribs, best or gentlemen’s houses. ― Beggar’s Cant.
1873		Sl. Dict.