Green’s Dictionary of Slang

nec ultra n.

[Lat. nec ultra, and not beyond; the line beyond which one might not go was Temple Bar, the line between the West End and the City]

(UK society) the West End of London, thus the fashionable world.

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D. Jerrold Story of a Feather Ch. ix: To the Countess Blushrose, Nature herself had written Nec Ultra on the west side of Temple Bar.
[UK]J. Ware Passing Eng. of the Victorian Era 181/1: Nec Ultra (Soc., 17–19 cent. ). West side of Temple Bar.