Green’s Dictionary of Slang

Countess of Puddle-dock n.

also Duchess of Puddle-dock
[Puddle Dock in London, now the site of the Mermaid Theatre, but orig. a large stagnant pool off the River Thames]

a self-appointed but spurious aristocrat.

[UK]T. Shadwell Epsom Wells II i: Stinking Town! I had rather be Countess of Puddle-dock, than Queen of Sussex.
[UK]Swift Polite Conversation 26: nev.: I promised to squire the Countess to her Box. miss.: The Countess of Puddledock, I suppose.