Green’s Dictionary of Slang

(UK Und.) a shabby person; an unpleasant, deceitful landlord.

a.1790		H.T. Potter New Dict. Cant (1795) n.p.: mumbling-cove an ill-natured shabby fellow, a sneaking landlord.
1809		G. Andrewes Dict. Sl. and Cant.
1848		Flash Dict. in Sinks of London Laid Open 116: Mumbling cove, a sturdy ill-natured landlord, shabby fellow.