Green’s Dictionary of Slang

sixpence (2½p).

[1663		J. Wilson Cheats II iv: Irish beef, by this good Tilbury – nothing but sheep’s heads and Irish beef].
1796		Grose Classical Dict. of the Vulgar Tongue (3rd edn).
1812		Vaux Vocab. of the Flash Lang.
1822		Life and Trial of James Mackcoull 27: I have had my hand in fifty pockets, and curse me if I touched a tilbury!
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc.