Mesopotamia, n. — Green’s Dictionary of Slang

Mesopotamia n.

[SE Mesopotamia, the land between the rivers Tigris and Euphrates, lit. ‘between the rivers’; although, much earlier, the Westbourne River once meandered through Belgravia, thus rendering the area ‘between’ that and the Thames, the implication is less geographical than racist; the Belgravia area was seen as the home of newly rich Jews. Oxford University jargon use is geographical, referring to that area of Oxford between the rivers Cherwell and Isis]

Belgravia.

1864		E. Yates Broken to Harness (1873) xv 143: A house in Great Adullam Street, Macpelah Square, in that district of London whilom [sic] known as Mesopotamia [F&H].
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict. 225: Mesopotamia a name given to Eaton Square and neighbourhood when first built. This part was also called Cubitopolis. ― Fashionable slang.