Green’s Dictionary of Slang

Tilbury (docker) n.

[rhy. sl. = knocker n.1 (7); ult. Tilbury docks (in East London)]

(UK prison) a prisoner who does not pay his debts.

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[UK](con. 1970s) N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 199: Those who did not pay their debts were known as ‘knockers’, or Tilbury dockers in rhyming slang. A reputation as a Tilbury would follow you everywhere.